Hi emkoxinh and welcome back!

Introduction

You wrote:

Many international conferences have been recently carried out to find solution for heavily polluted environment relating to high number of car use.

Really? Where? What dates? What was the result? When is the next one? Was there a keynote speaker? Who held the conference? Who sponsored it?

Scientists/Psychologists/Researchers/Famous experts/Reports/Conferences/blah blah blah... Forget Them!

Please, everyone: no research, no scientists, no surveys, no polls, no conferences, no recent papers, no recent reports, no recent newspaper articles, and no reports just published. This is YOUR opinion essay. It’s not Task 1 where we analyze data. We don’t need science or pseudo-made-up imagined science to justify or back up our ideas. Just give YOUR ideas or describe the situation. Forget about researchers and scientists and experts and famous psychologists.

Shorten

This sentence is good, but very long:

This can be a effective solution but I think that it also leads to some unwanted consequences and more measures should be taken into consideration in addition to the introduction of tax. (32 words)

It’s too long. Try to make all your sentences less than 20 or 25 words. Aim for an average length of about 12-15 words per sentence. Let’s break it up.

Raising taxes on fuel can be an effective solution. However, it can have unwanted consequences. I believe more measures should be taken in addition to the introduction of higher taxes. (30 words, 3 sentences, average 10 words per sentence)

You wrote:

It is undeniable that no sooner is higher taxation implemented than car owners instantly reduce their frequence of driving car due to the economic reason. (25 words)

Shorten, remove the tired phrase “it is undeniable”

Higher fuel costs do reduce mileage  OR  
Higher fuel prices definitely mean fewer car journeys.

Unnecessary words:

Facts have shown that Chinese residents who travel to work by bicycles and underground trains, instead of cars, save a lot of money per month.

Ideas/Logic

You wrote:

However, it is increasing tax on private cars that partially results in the inflation in a country because of mounting costs of transporting goods

Are private cars (family cars) used for transporting goods? Trucks and lorries and vans are usually used to transport goods, not private cars. If private cars are used to transport goods in your country, you need to explain this to the reader.

Shorten

This monster is 37 words long. It has to be shortened.

Take Vietnam for example, since high taxation was accepted, prices of varied merchandises have been one and a half or even two times higher, putting the economy as well as people’s life here in a difficult stage.

Here are some rewrites. Keep sentences short.  

• Take Vietnam for example. When the tax on fuel went up, the price of many goods doubled. This caused a lot of hardship for ordinary people. (26 words, three sentences, average 8.6 words per sentence)
   
• Take Vietnam for example. After a recent fuel increase, the price of many goods doubled, causing a lot of hardship for ordinary people. (23 words, two sentences, average 11.5 words per sentence)
   
• A recent fuel increase in Vietnam, for example, resulted in the price of many goods doubling.  This caused a lot of hardship for ordinary people. (25 words, two sentences, average 12.5 words per sentence)
   
• When fuels taxes were increased in Vietnam recently, for example, inflation shot up, damaging the economy and causing hardship for ordinary people. (22 words, one sentences, average 22 words per sentence)

Here's another monster:

Secondly, in long term, cars using environmentally friendly energy is one of the crucial and inevitable keys to impede pollutants emitted into the atmosphere. (24 words)

Here are two possible rewrites:

Secondly, environmentally-friendly cars are key to reducing air pollution (10 words)  OR 
Secondly, environmentally-friendly cars are crucial for reducing air pollution. (9 words)

Variety of sentence structures

I like this sentence:

If taxing more on petrol and diesel fuel is not the most sufficient answer, so what other strategies should be taken into account?

It just needs a small edit:

• If higher taxes on petrol and diesel are not the answer, what other strategies should be taken into account?  OR
• So if more fuel taxes are not the answer, what other strategies should be used?

 Overall, some good stuff here, but you just need to watch those long sentences!