Abstract: The East Asian monsoon exerts significant impacts on the climate and environment of China. Previous research (Wang, 2001) has focused mostly on monsoon circulation and the summer precipitation in specific areas, although few studies have been conducted on the monsoon area and its precipitation in China (Ding et al., 2009). In study, we employed four observed precipitation datasets, including the high-resolution gridded dataset based on 2416 observation stations across China, to analyze monsoon area, its northwestern boundary, and monsoon precipitation intensity for 1961-2009. The results show that the monsoon area accounts for approximately 60% of mainland China and generally contracts during the period. Monsoon precipitation exhibits apparently interannual and interdecadal variabilities. The average intensity of monsoon precipitation is 4.46 mm d^-1. The region between the eastern and western boundary of the northwestern monsoon area belongs to a typical dry-wet transitional zone. The northwestern boundary advances westward south of 40°N (-0.026%) and retreats eastward north of 40°N (0.041%), owing mainly to changes in thermal contrast, atmospheric circulation, and water vapor flux and its divergence.