The space time distribution features and large scale atmospheric circulation of the 2011 autumn rainfall in West China are analyzed to study the physical mechanisms of autumn rainfall. The results show that there were more rainy days, stronger raining processes and longer duration than normal in northern West China in September 2011. The 500 hPa circulation analysis shows that there was a quasi stationary ridge near Lake Balkhash, from which the cold air was combined constantly with the warm and humid southeast air in the southwest side of the subtropical high and with the southwest air from the Bay of Bengal. The physical analysis shows that there was a strong energy frontal zone in the north of West China, which was strengthened because the cold air from the east area entered so that the instability energy burst out, thus triggering the rainstorm in West China.