The circulation patterns corresponding to severe drought and flood years of North China are studied and the years are fixed by making use of the method based on Z index.The key areas of SST affecting North China rainfall in summer are found by means of correlation analysis, which are located in the equatorial East and Middle Pacific and high and middle latitudes of North Pacific. Numerical experiments are conducted in order to study the mechanism of SST affecting North China summer rainfall in the two areas.As a result,some meaningful outcome are obtained.Besides,the possible mechanism responsible for the anomaly of North China summer rainfall is investigated.