Abstract: The relations between change of θse and rainy season of Yunnan are studied.The results show that θse can better describes the characteristic of the activity of tropical monsoon air mass.With season shifting from spring to summer,the tropical monsoon air mass moves northward and westward.If the meridional moisture transportation of the Bay of Bengal is strong(weak),the rainy season of Yunnan begins early(late).The climate standard and annual standard of monsoon establishment of Yunnan are defined by using θse and rainfall of Yunnan,separately.Finally,a question is put forward:can Changes of θse of upper troposphere predict monsoon establishment of Yunnan.