Abstract: Using Princeton University's 1961 to 2010 atmospheric external forcing data and NCAR's CLM4.0 (Community Land Model 4.0), an off-line simulation was conducted of the land surface process in Southwest China. Results show that there are sharp distinctions between the precipitation characteristics in Southwest China's wet and dry seasons. During the monsoon season, total precipitation decreases northeastward from Burma and India, while it decreases westward from the Hubei and Hunan provinces in the non-monsoon season. With respect to the annual mean, only about 16.7% of the precipitation in the Southwest China is directly intercepted by the canopy, and of the remaining proportion reaching the ground, about 60.5% infiltrates the soil, approximately 17.1% flows out in runoff, and a small amount evaporats re-enter into the atmosphere. The distributions of the primary hydrological processes are similar to that of precipitation. Canopy interception, surface runoff, and canopy evaporation rarely varies during monsoon and non-monsoon seasons. However, underground drainage and surface evaporation are both significantly greater in the non-monsoon season than during the monsoon season, while infiltration shows just the opposite. In the non-monsoon season, smaller levels of infiltration, higher evaporation rates, and higher underground drainage together result in significant loss of land water in Southwest China, and may play an important role in causing the region's spring drought.