Abstract:Based on autumn (September to November) rainy days of 81 stations in Guizhou from 1964 to 2013 and National Center for Environmental Prediction/Atmospheric Research Center (NCEP/NCAR) reanalysis data, the spatio temporal variation of autumn rainy days in Guizhou and its relation with atmospheric circulation were analyzed with Morlet wavelet and synthetic analysis, and other ways. The results show that the autumn rainy days in Guizhou are increased gradually from southeast to northwest between 30.0 d and 52.3 d. Mean autumn rainy days in Guizhou are about 40.5 d. There is the decreasing trend of autumn rainy days in the past 50 years, and its regression coefficient is -1.9 d/10 a. There is an abrupt change around 1987 for the autumn rainy days, which are more than normal in 1964-1987 but less than normal in 1988-2013. Since 1997, the decreasing trend is the most obvious. The autumn rainy days in the past 50 years have obviously quasi 5 year and 2-3 year oscillation periods over Guizhou, of which the 5 year oscillation is the most obvious, 2-3 year periodic oscillation is the second. At the same time, when the autumn rainy days are more over Guizhou, the South China Sea water vapor flux converges, the cold air activity is more active in the high latitudes, the East Asian trough is strong and the trough and ridge over the low latitudes deepen slightly, Guizhou lies in front of the India Burma trough and, the strong southern airflow is in favor of the intersection of warm and cold airs, thus creating the frequent rainy weather; and vice versa.