Using the monthly mean reanalysis data of the NCEP/NCAR, and the data of monthly mean SST by NOAA during 1961 to 2008, and the precipitation in spring in Chongqing from 1961 to 2008, the relationship between the spring rainfall in Chongqing and the early autumn SST is analyzed. The result shows that a close negative/positive correlation exists between the spring rainfall in Chongqing and the early autumn SST in the neighborhood of the North Pacific drift (20°-40°N，165°E-140°W)/Alaska current (40°-60°N，165°E-140°W), respectively. When the early autumn SST of the subtropical North Pacific Ocean is anomalously high, and that of middlehigh latitudes is anomalously low, then the spring rainfall in Chongqing is more. On the other hand, when the early autumn SST of the subtropical North Pacific Ocean is anomalously low, 〖JP2〗and that of middlehigh latitudes is anomalously high, then the spring rainfall in Chongqing is less. A discriminate index for diagnosing and forecasting the spring rainfall is defined according to the correlation distribution characteristics. This index stands for the opposed anomalous SST conditions of the south and north areas in the North Pacific Ocean. It has important synoptic climatological significance, and can diagnose and forecast the spring rainfall in Chongqing. The index leads to the anomalies of eigenvalues of spring 500 hPa height all through, which makes the spring rainfall in Chongqing anomalous.