Based on the NCEP/NCAR,ERA-40 reanalysis datasets and 160 stations precipitation data in China in summer(July and August),by means of correlation analysis,composite analysis and other methods,the interannual relationship between Mascarene High(MH) and summer precipitation in North China and it's interdecadal variability are analyzed.Results show that there is significant negative correlation between the MH and summer precipitation in North China in interannual time scale and that this negative correlation relationship began to diminish since 1974.During the stronger period(1951-1973),significant negative correlation center between the MH and summer precipitation over eastern China was mainly located in North China,while during the weaker period(1974-2011),the negative correlation between the MH and summer precipitation over North China became weaker,and significant positive correlation center was observed in the middle and lower reaches of the Yangtze river.The cause for interdecadal variability between MH and summer precipitation in North China is as follows:when Eastern China is(not) influenced by the stronger anomalous south wind coming from MH,summer precipitation in North China is more(less),and the relationship between MH and summer precipitation in North China is in stronger(weaker) period.The interdecadal variability of inter-annual relationship between MH and summer precipitation in North China is one of the causes for the floods in Southeast China and droughts in Northeast China since the mid-1970s.