Abstract: Develop the standard of rainy season beginning time of Yunnan province by statistics of the first significant precipitation data in the period after the conversion of the dry season to the rainy season from 1952 to 2012.In the 62 years,the time of rainy season beginning of Yuxi was very unstable.Normal year(5 days before or after May 18th) only accounted for 24.2%.75.8% of years was too early or too late.The difference between the earliest year and the latest year was 76 days.By analysis of the relationship between the start of the rainy season and atmospheric circulation,we found that the correlation between the 500hPa height filed of some area in January to April,June to August and October to December of previous year and the beginning of rainy season was good.When the height filed of Mariana Islands,Bay of Bengal,Arabian Sea,northern Canada,the East China Sea and Iran to the Qinghai-Tibet Plateau became higher,and the height filed of Western Europe north of the south bank of the East Siberian Sea,Svalbard,Europe Volga became lower,then the start of rainy season was normal or early,or vice versa.When the phenomenon of La Ni〖AKn~〗a occurred,polar vortex tended to east or Tibetan high pressure was powerful,then the start of rainy season was normal or early in next year.When the phenomenon of El Nino occurred,polar vortex tended to west or Asian zonal circulation was weak,then the start of rainy season was late or very late in next year.