Based on the daily precipitation data from 740 stations in China and NCEP／NCAR daily reanalysis datasets,the interdecadal variability of largescale precipitation conditions over North China during rainy seasons is analyzed by means of composite analysis methods.The results show that:with a turning point from flood period to dry period in 1978,anomalous moisture budget over North China changed from south boundary and west boundary to north boundary and east boundary and thus made water vapor become divergent and absent from convergent and abundant.Warm and moisture air mass from ocean could reach the north area of North China or even its northern border before 1978,but it could only reach the south bank after 1978.The interaction between the cold and warm moisture air mass along the Taihang Mountain became weaker.In addition,anomalous upward motion became anomalous downward motion over the North China;areal average vorticity changed from two layers structure(positive vorticity in the low levels and negative vorticity in the high levels) to three layers structure(negative vorticity in the middle and lower troposphere,positive vorticity in the middle and negative vorticity in up troposphere) and the value of total vorticity became smaller.Vertical configurations of areal average divergence and vertical velocity presented no conspicuous interdecadal variability,but their values all became smaller.