HI Christyzhongs and thanks for this essay!

The essay is clear and well organized. Some good ideas, and good use of paragraphs.

I would change two things: the thesis sentence and the first sentence in the conclusion.

Thesis Sentene

The thesis sentence and the sentence before it (“Is it a positive development?  Personally, I feel that whether it is good or bad depends on the individual’s attitude. “) could be used in a million essays. Why lose this opportunity to make it specific and show the examiner that you understand the topic and to show some extra task-related vocab?

Here’s one possible rewrite:

I think consumers have to weigh up having an increased choice of food with the possible effect on local farmers.

OR

While most people enjoy having a variety of food from different countries, we also need to think about the environmental cost and the effect on farmers in our own country.

You didn’t develop the theme of the ‘individual’s attitude’ in your sentence.   Make sure you develop and support all your ideas. Even though the sentence looks like a generic sentence, you could have made it into a main point in your essay, but you missed this opportunity.

Conclusion

The first sentence in your conclusion says that air transport is good. However, the previous sentence said it has a bad effect on the environment. This sequence of sentences of doesn’t make sense! Have a look at the official descriptors for IELTS Task 2 Writing (public version) here, under Coherence and Cohesion. Band 6 requires that the candidate “arranges information and ideas coherently” -  make sure that you mark changes in ideas and don't make sudden switches without explanation.  

Use ‘although’ or ‘despite this’ or something to show the change: 

In conclusion, although importing food can be harmful to the environment and affect the livelihood of local farmers, it provides…

Word Choice/Word Form/Usage

• We can easy to find American Grapes,Thailandrice, mango etc. → It is easy to find products such as X, Y or Z.   OR    We can easily find American grapes, Thai rice, or mangoes from Pakistan…
   
• more choice on foods  → more choice of foods   OR   imports give people more choice
   
• a more balance diet → a more balanced diet 
   
• It also provides more job opportunities for some industries, like the agricultural, transportation and trade etc → It also provides more job opportunities for industries such as agriculture, transportation and trade. 
   
• It is easy to image that → It is easy to imagine that
   
• That result the local products are dull of sale → The result would be that local products would have lower sales.   OR   As a result, sales of local products might drop.
   
• using air transport to export or import agriculture products is good to both countries and their citizens. → is good for
   
• At the mean time → in the meantime

Articles/Plurals

A few small problems with unnecessary articles:

• That’s because the air transport is widely used → That’s because air transport is widely used
• importing the agriculture products → importing agricultural products
• vegetables are hard to grow in some desert area → vegetables are hard to grow in some desert areas
• different kind of vegetables or fruits contains different ingredient →  different kinds of vegetables or fruits contain different ingredients
• selling the imported products may have negative impact → selling imported products may have a negative impact
• air transport use massive amount of fuel → air transport uses a massive amount of fuel

Punctuation: Run-On sentence

The last part of this sentence should be separate.

• Selling imported products may have a negative impact on the local agricultural that’s why some people think it is unjustified.

See more about Read more about Fragments , Run-On Sentences, and  Comma Splices. Here’s one possible rewrite:

Selling imported products may have a negative impact on the local agriculture. Because of this, some people think it is unjustified.   OR

Some people think imports are not acceptable because of their impact on local agriculture.

Overall, a nice clear essay with good supported ideas. Just work hard on a good thesis sentence, and make sure your conclusion summarizes the body of your essay.