In this paper,an index of land-sea thermal difference(ILSTD ) is developed with the relationship among index,th e east Asian monsoon circulation and the summer rainfall in China discussed.The results are as follows:1)ILSTD can reflect the interannual variation of the summer rainfall anomaly over eastern China,especially in north China and Huaihe valleys and the mid/low reaches of the Yangtze River.In the years of strong ILSTD ,rainfall belt is mainly located over north part of China,and obvious drought emerges in Huaihe valleys and the mid/low reaches of the Yangtze River.However,during the weak years,summer rainfall belt is largely locat ed over the mid/low reaches of the Yangtze River.2)The index can identify the pa ttern of atmospheric circulation impacting rainfall in eastern China,especially for the position and strength of west Pacific subtropical high in summer.In the strong(weak) index years,the circulation fields at 500hPa in the n orthern hemisphere can be used to explain the features of the strength changes o f the summer monsoon and the summer rainfall anomaly.