By using the data of precipitation and sunshine duration in Sichuan,Chongqing,Yunnan and Guizhou over Southwest China,the monitoring indexes of autumn rainfall over Southwest China for extreme weather and climate events are discussed. An autumn rain event is defined as: with the number of successive rainy days greater than 5; the amounts of precipitation more than 01 mm; and the sunshine duration less than 01 hour. This index can describe the disaster characteristics of continuity and less sunshine of autumn rain events over Southwest China.The results indicate that autumn rain events in Southwest China happen mainly in the middle and south of the Sichuan basin,western Chongqing,northeastern Yunnan and northern Guizhou, with the occurrence frequency being more than 16 times per year in the central area of the region and the average number of rainy days being over 11 The intensity of autumn rainfall over Southwest China exhibits a downtrend with fluctuation.Combining with the simultaneous NCEP/NCAR data of the geopotential height fields, water vapor field and wind data, the causes of autumn rainfall over Southwest China are systematically analyzed. The results indicate that in severe autumn rain years, the pressure at 500 hPa in the polar zone is quite high, and the subtropical ridge line is northward and the Indian and Burma trough is deeper. In the area where the autumn rain is severe,there is an obvious water vapor convergence at 850 hPa over Southwest China. There is an upward motion working along with the vertical latitudinal and longitudinal circulation.