Daily meteorological data of Sichuan Basin and NCEP/ NCAR reanalysis data are employed to diagnose the influences of East Asian and plateau summer monsoon on the summer rainfall of Sichuan Basin. The results show that the summer rainfall series of the western and eastern basin and the correlation distribution of summer rainfall over the whole China have similar distribution with the rain pattern Ⅰand Ⅱ respectively. To further understand the effect of East Asian and plateau summer monsoon on the rainfall of the basin, regressive analysis is performed. First the circulation field related to East Asian summer monsoon is obtained, then after the part of East Asian summer monsoon is removed from the circulation field using the regression method, the circulation field related to plateau summer monsoon is yielded, which is statistically independent of East Asian summer monsoon. Using the 1961 and 1998 circulation fields as examples to analyze the influences of East Asian and plateau summer monsoon, it is found that both East Asian summer monsoon and plateau summer monsoon have important influences on the rainfall of Sichuan Basin, of which the rainfall of western part is mainly related to plateau monsoon, and the summer rainfall of eastern part mainly is related to both East Asian and plateau summer monsoon, but East Asian monsoon is predominant.