Abstract: Applying the data of the monthly precipitation in Yunnan 124 stations from 1961 to 2012 and the monthly reanalysis data provided by the NCEP/NCAR,the variation of the precipitation in autumn over Yunnan and its physical causes have been studied.The results show as following:There are obvious differences in the distribution of precipitation over Yunnan.The precipitation in the west and south of the Ailao Mountain are more than that in the east and north.The trend of precipitation in the autumn tends to increase in the western and northwest of Yunnan,but decrease in the eastern and southwest region.The spatial variation of the autumn precipitation shows the consistency phase varies.The second main mode of the precipitation in autumn over Yunnan presents an out-of-phase oscillation between the area in northwest and the area in southeast of Yunnan.The precipitation in autumn over Yunnan presents intimate correlation with atmospheric circulation.The strength of the surface cold high,the strength of the polar vortex,the Ural block high and the westerly trough in BOB in the 500hPa height field,the abnormity of southerly in the 700hPa and the temperature in 850 hPa temperature field over Yunnan have obvious effects on the autumn precipitation in Yunnan.The composition analysis results show that the source of vapor transportation and the water content vary in rainy and drought years.In the rainy years,the sources of the vapor transportation are from the Indian Ocean and the Bay of Bengal and from the Western Pacific and the South China Sea;both the water-vapor content and the water vapor saturation are higher.In the drought years,the source of the vapor transportation is from the westerly transport in the middle latitude; both the water-vapor content and the water vapor saturation are lower.The configuration of divergence field at lower level and higher level and the vertical movement over Yunnan play an activive role in precipitation.The convergence at lower level companied with divergence at higher level and significant vertical upward movement result in the rainy years.It has been found that the precipitation in autumn over Yunnan has also intimate correlation with SST anomalies.When the SST in the east of the Hawaiian Islands is higher,the SST from the East of Malaysia to the Guam Island will be lower,the precipitation in autumn over Yunnan will increase.