In this article,based on the rainfall data over North China in May,atmospheric circulation data(NCEP)and the sea surface temperature data(SST),the methods of correlation analysis and composition analysis are used to study total,spatial and temporal distribution characteristics of the rainfall in May over North China,investigate correlation with interannual variation of sea surface temperature and atmospheric circulation ,and analyse mechanism of influence.It indicates:there is interannual variable characteristics of the rainfall in May,the years of less rainfall are far more than that of more rainfall.There is less difference between the rainfall of the years of less rainfall and average value,whereas there is more difference between the rainfall of the years of more rainfall and average value.There is significant positive correlation between interannual variation of atmospheric circulation(200 hPa) in area （25～50 °N，110～145 °E） and that of the rainfall in May.There is significant positive correlation between interannual variation of former low level atmospheric circulation and that of the rainfall in May.The variation of the Rossby wave moving westward in the middle latitude and Equatorial Indian Ocean are the important causes of interannual variation of the rainfall in May over North China.