As his chemistry teacher during his high-school study, I am very pleasant to recommend Mr. Zong Zhen to your prestigious institution.
After taking the very competitive examinations of the province high-school qualification test, Mr. Zong was selected as one of the best candidates. Afterwards, He was ranked the first in the national chemistry contest(contest是指考试类的竞赛，而competition指各种比赛)(不过你的文中没有说清楚，是在你们学校里最好？还是所有竞赛的选手中的最好)。最后一句话就是说你自己化学排在5%不用写出来，因为太罗嗦
先跟你改了前两段，等会做完实验再帮你改改其他的
Although he didn’t get a very nice result in the chemistry competition held on 13th September, I’ve never doubted his grades and achievements in chemistry（本人觉得这是一句废话,可以删掉）. Furthermore(表明你跟一般学生不一样的地方)，as a high school student, he has learnt “Inorganic Chemistry” and “Organic Chemistry” on his own，which can not only show his distinguished excellence among his peers, but also demonstrate his great passion to chemistry.
During the(这里没有冠词的) more than two year’s（应改为years’）study, he appears (过去式，) a lot of scholastic aptitudes and good personalities. 但是你想说的是展示，所以不能用appear,刚刚上一段用了show和demonstrate这里为了避免重复，这句话可以改为：During more than two years’ study, he proves to be a student of academic potential and good personality:
He is full of imagination and do(三人称单数) have a capacity for abstract reasoning and analytical thinking（你想说什*么，不了解，是想说抽象思维和分析能力？） He always has attractive ideas about what he has learnt and often discusses them（改为shares） with his classmates. He was awarded “Model Student of the school” almost every term（这句话比较中式翻译，其实也不是不能说，而是应该放在收尾的地方，而且要换一种说法， 如Based on his outstanding performance, he was awarded “Prize of Excellent Student” every semester in our school )
To my knowledge, the enthusiastic student （改为this young man） also has a sense of responsibility. He used to be the leader of (改为 he used to be in charge of) the school’s Table Tennis Club, which is one of the best clubs in our school(后面的一个最好的俱乐部根本没必要提) 这一段其实讲的是社会活动类，应该放在下面的一段中。
As far as I am concerned, he is not only strong in study, but also in sports and social activities.（这句话的前半段太罗嗦，西方人的思维差别就是要做到尽量简练，所以这句话可以改为： Apart from his educational strength, he is good at sports and loves participating social activities.） He has won the first prize in a table tennis competition held in our school together with other two students in his class (这句话像你这么摆，就显得很长，读起来费劲，可以换成： Together with other two classmates, he has won the first prize in a table tennis competition in our school). He does （时态）voluntary job as a librarian and a water quality monitoring staff during vocations.（这句话可以改为，As far as I know, he ever worked voluntarily as a librarian and also helped to monitor water quality in(在哪里做的) during his vocation(作抽象名词的时候不可数). In everyday life, he is good at adjusting his emotions(这点可要可不要) and goes well with all his classmates. (我建议这句话写成，besides, he gets along very well with his classmates(如果你说all,我觉得有点假)
楼主 
...
