Based on the monthly mean temperature and precipitation data of 155 stations covering 1961-1999 in eastern and northern China,and using the Thornthwaite formula,the water requirement and the moisture index in study area are calculated in this paper.The-20 and 0 moisture index isolines are defined as the front and back boundaries of monsoon's boundary zone.The boundaries' interdecadal positions and their fluctuations are also analyzed,and results show that in the 39 years,the motion of the monsoon's boundaries in the east of China has an obvious regional character,and the fluctuation of the back boundary also has a conspicuous interdecadal variability.The interdecadal variation characteristics of rainfall in the study area are analyzed too,and it is found that the trends of precipitation in the three subareas,i.e.the east of Northwest China,North China,and Northeast China,are generally in agreement with the respective trends of the boundary fluctuations of monsoon.