Abstract: To grasp the change trend of main chemical composition of Yunnan big leaf species sun dried green tea, analyze the optimum processing suitability, and provide the theory basis for the production of Pu'er tea, the author conducted an experiment on the content change of the main chemical composition of Yunnan big leaf species sun-dry tea which were produced between March and October in 2013. The results showed that tea polyphenols content increased progressively from March to July, and it showed a decreasing trend from July to October, the highest record appeared in July which reached 41.77%. Catechins content presented an increasing trend from March to August, and it showed a decreasing trend from August to October, the highest record was 14.5% which appeared in August. Water extract content increased progressively from March to July, and it decreased progressively from July to October, the highest record appeared in July which reached 51.74%. The amino acid content presented a decreasing trend from March to June, and it showed an increasing trend from June to October, the lowest record appeared in June which was 2.45%. Caffeine content presented an increasing trend from March to July, and it showed a decreasing trend from July to October, the highest record was 3.82% which appeared in July.