The drought/flood index of precipitation in summer was determined based on the first component of precipitation total amount from June to August for 65 stations. Then, the relationship between the preceding South China Sea SST and the drought/flood in the middle and lower reaches of the Chang jiang River valleys and the southeastern region were studied by using the correlation matrix. The relationships were shown principally by the abnormal drought/flood years, the correlation of the preceding SST with the drought/flood were persistent for a certain period and indicated that the preceding SST contributed significantly to the formation of drought/flood in the middle and lower reaches of the Chang jiang River valleys. The results provide the reference for long-range forecast of drought/flood.