Based on the 3 years continuous locating observation, this paper discussed the precipitation pattern and its relations to the runoff and soil erosion. The results show that the raining are characterized of obvious wet and dry seasons through the year, and the rainfall in average up to 1 019. 6mm per year, with especially heavy rains between May and October of 827. 7 mm, which account for 81.18% of the total year rainfalls. The formation of the runoff is saturated runoff in trial watershed, furthermore, the uneven distribution, the over concentration of the precipitation and consequential heavy rain and hard rain, are the principal factors that resulted in the runoff and erosion. Forested lands have a notable effect on cutting the slope runoff and erosion compared to the naked land. However, the reducing benefits of runoff and erosion of forests has a highly correlation with the tree species' biological, ecological property and its stands structural status.