You asked about one topic per paragraph, and yes, I agree it's better to separate them. There is no fixed layout in the official descriptors for IELTS Task 2 Writing (public version) here, so it doesn't matter whether you choose 3773, 3553 or any other layout. 

The important thing is to use paragraphs. Have a look at what the descriptors say for Bands 7, 8, and 9. They want ONE clear topic per paragraph.

As regards your second question, don't worry about it at the moment. Many of the questions in textbooks or floating around the internet are not exact copies of IELTS questions. When you get the question, underline like crazy, highlight, draw arrows, draw circles, write related words, synonyms, oppposites; change nouns into verbs and verbs into adjectives. Play for at least five minutes until you are sure of the question, and keep going back to it until you have a plan for each paragraph. Have examples for each idea.

Here's an example of a topic with related words and brainstorm for this topic

With the increasing number of people in cities, many people do not know their neighbors and the sense of community is lost. What is causing this? How can we turn it around?

I don't know how accurate this version of the question is, but does anyone want to try?  If you do, just open a new topic.

Whatever you do, don't start to write without ideas: that's like trying to fly without enough fuel and will have the same result -  a lot of flapping around and going nowhere but down.

First, about the question of paragraph. I've read some articles given by IELTS's examiners, and find they may prefer one paragraph containing one argument. This makes every argument could be easily distinguished. So what's your suggestion for the real IELTS.

Secondly, it seems that the biggest problem of my essay is I cannot meet all requirements of the question, isn' it? I'm wandering is it also the biggest problem I must solve if I  want to get band 7 in the IELTS writing? In my fisrt essay subscribed, you said I didn't  fully develop all ideas. DoIi have the same problem in this one?

Again, thanks a lot.

Thanks to DavidLee for his comments, too!

One important point that you haven’t really discussed is why rich countries should help poorer ones. You have some nice phrases in your intro (“give hope” and “shoulder responsibility”), but why should the richer countries do this? What’s in it for them? You’ve described a lot of benefits for the target country, but none for the donor. 

Here's the question again:

Improvements in health, education and trade are essential for the development of poorer nations. However, the government should take more responsibility for helping the poorer nations in such areas. 

You've discussed health but not really education (just two words - 'educational resources' ) and not trade, unless you mean the corporations. This needs to tie back to the question more. 

Real IELTS questions often look similar to the ones in IELTS textbooks, but are slightly different, or have a subtle twist. Make sure you deal with all parts of the question rather than answer a standard "rich-countries-aid-poor-countries" question.

Coherence and Cohesion

You wrote:

In current news, we can always hear a phrase: the international humanitarian assistance, which is used to give a hand to countries suffering hardship. (24 words, 1 sentence)

The ‘which’ is not correct here.  Let’s avoid the problem by simplifying and shortening the sentence, or breaking it up:

 We often hear about humanitarian assistance in the news. Countries give a hand to other countries suffering hardship. (18 words, 9 words per sentence on average)  OR

International humanitarian assistance means countries helping other countries which are suffering hardship. (12 words)

 Word Choice/Word Form/Usage

• earning bread through their own effort → earning money
• it cannot be ignore that → it cannot be ignored that
• in terms of their health and education, etc.  → in terms of their health and education. [don’t use ‘etc -  spotted by David]
• improves local environmental sanitation → improves the local environment? Improves sanitation? Improves sanitation and the environment? [unclear]
• Besides, serious supervision system should be established to ensure the assistance is correctly utilized. → However, systems should be established to ensure the assistance is correctly utilized.
• This means that in some aided countries, the international aid cannot be allocated to average people. → This means that in some recipient countries, international aid is not allocated to affected people.   OR This means that in some countries, aid does not reach the people who need it. (15 words)
• Instead, the officials become the beneficiary of it selfishly. → Instead, the officials become the beneficiary.  

Shorten/Simplify

You wrote:

• However, it cannot be ignore that there appear some evidence to support the view that the poorer the country is, the more corrupted the government is. (26 words)

Why all the introductory remarks? They add nothing. Here’s your sentence:

Often, however, the poorer the country, the more corrupt the government. (11 words)

Overall, it's quite a good essay and ideas generally flow well. Some good sentences: I like this one:

Such assistance can really give hope to the people in those countries and help them to develop themselves

DavidLee's comments

I agree with some of his points (not all  - some of the minor grammar points he finds are fine in your original), especially the need for a thesis and maybe some reorganization.

I agree with DavidLee that you should have a thesis sentence in your intro. You can read more about Thesis sentences here. It helps you and the reader to know what is coming in your essay.

David had an interesting point about you not needing a paragraph. He joined your paragraph two and three together. 

What do you think? I see his point: he's putting two related ideas together (the benefits of helping other countries), and then you would have one paragraph with the negative aspects of helping some countries.

Again, thanks to you both.

In current news, we can always hear a phrase: the international humanitarian assistance, which is used to(used to means u have done sth before,change it to which means) giving a hand to countries which are suffering hardship. Such assistance can really give the hope to the people in those countries and help to develop themselves (a bit weird, maybe this way would be better, give the hope to the people and develop the country) , so richer countries should shoulder(its ok, but i guess undertake would be better) this responsibility.(You need to write a thesis sentence here)

People of(from) many countries in Africa and Middle East area live in a poor life, in terms of their health and education, etc. (dont write e.g. or etc. in the essay)The help from richer countries, not only financially, but technically, would improves the local environmental sanitation and provides educational resources. Most importantly, the workers and volunteers from assistant countries help them to raise the public awareness of the serious diseases, and tell them how to avoid from being affected.(The sentence is too long, just write helping them to pay attention and avoid the serious diseases) These activities could largely reduce the mortality rate.(There is no need to have another paragraph)In addition, with the aid offrom some rich countries(if u wanna use of, i ll comprehend they receive the developed nations to help them developing their own country). international corporations are established in those undeveloped countries, exploiting and processing natural resources. As a result, more local residents get employed, earning bread through their own efforts. Also, the local resources are made the most using efficiently of instead of being wasted.

However, it cannot be ignore that there appearare some evidence to support the view that the poorer the country is, the more corrupted the government is. This means that in some aided(what this means? ) countries, the international aid cannot be allocated to average people. Instead, the officials become the beneficiary of it selfishly. This is, sometimes, the excuse used by richer countries to refuse to offer help.

In conclusion, I agree that richer countries should make efforts to help the poorer ones (poverty). Besides, serious supervision system should be established to ensure the assistance is correctly utilized.

In current news, we can always hear a phrase: the international humanitarian assistance, which is used to give a hand to countries suffering hardship. Such assistance can really give hope to the people in those countries and help to develop themselves, so richer countries should shoulder this responsibility.

People of many countries in Africa andMiddle Eastarea live a poor life, in terms of their health and education, etc. The help from richer countries, not only financially, but technically, improves local environmental sanitation and provides educational resources. Most importantly, the workers and volunteers from assistant countries help raise the public awareness of serious diseases and tell them how to avoid being affected. These activities could largely reduce the morality rate.

In addition, with the aid of some rich countries, international corporations are established in those undeveloped countries, exploiting and processing natural resources. As a result, more local residents get employed, earning bread through their own effort. Also, the local resources are made the most of instead of being wasted.

However, it cannot be ignore that there appear some evidence to support the view that the poorer the country is, the more corrupted the government is. This means that in some aided countries, the international aid cannot be allocated to average people. Instead, the officials become the beneficiary of it selfishly. This is, sometimes, the excuse used by richer countries to refuse to offer help.

In conclusion, I agree that richer countries should make effort to help the poorer ones. Besides, serious supervision system should be established to ensure the assistance is correctly utilized.