The variation characteristics of precipitation in the dry season (from November to the following April) in the Southwest of China are investigated by using the observation data from 1961 to 2011. The results indicated that the precipitation during the dry season changed remarkably around 2000. The spatial distribution characteristics of the precipitation before 2000 was distinctively different from the characteristics after 2000. The rain was much less than normal and drought got worsened in the 21st century. Precipitation in Yunnan and its surrounding areas reduced significantly. The negative correlation between the rain of the dry season in Southwest and the western Pacific subtropical high (WPSH) strengthened rapidly in late 1990s. Meanwhile the feature of WPSH has shown markedly decadal enhancement since the 21st century. Its area has been growing, with intensity enhancing and position being farther western than normal. Enhancement of the relation between the rainfall during the dry season and WPSH and the decadal enhancement of WPSH, both contribute remarkably to the decline of the dryseason rainfall, and probably result in the frequent drought in the Southwest of China.