I have always been in the top 10 since my first year of primary school, and this record remained[if you have graduated - this is in the past] to my college graduation. I attended the Chinese Geography Olympiad (Fujian Province) in 2008, when I was in my second year of high school. I was awarded 'The Excellent Student Leader'[easier to read if its in quotes] in 2011 by our department and my university. This award has very strict requirements. Only Less than twenty students out of 1200 students [only write students once - either is fine] are awarded.

Though very successful in most of the time, there was one frustration. I graduated from high school in 2009 and took the Chinese College Entrance Examination the same year. However the exam result of one course turned out to be unreasonably (uncharacteristically?/surprisingly?)[unreasonable is not a good word to use - that says that it was unfair] bad, for which I still do not know the reason. [I would not write this - it is a little unprofessional perhaps]

You will see my version is very close to Gary's. 

Maybe between the two you can get more ideas.

I have always been in the top 10 since my first year of primary school and maintained this record remains to my college graduation. I attended the Chinese Geography Olympiad in Fujian Province in 2008 when I was in my second year of high school. I was awarded title of "The Excellent Student Leader" in 2011 by our department and(of?) my university. This award has very strict requirements. Only l Less than twenty students out of 1200 are receive this awarded.

Though very successful in most of the time, there was one frustration. I graduated from high school in 2009 and took the "Chinese College Entrance Examination" the same year. However the exam result of one course turned out to be unreasonably bad, the reason for which I still do not know the reason.

I would not use a comma before "And", though I know many Americans do this in lists.

If your language is formal, try to avoid brackets.

There is often debate about how many commas to use in English. In general many English natives use more commas than necessary, so using more will not usually be offensive.

if you capitalise "Chinese College Entrance Examination", you probably should have quotation marks.

The last comma from .."bad, the reason"... should probably be stronger, a full stop maybe. Sorry, I am not an expert at stops.