Based on the quantitative analyzing of the similar topographical characteristics and classification of Caijiahuan watershed and its 6 branches by system clustering analyze of MATLAB in the Loess Plateau, the western Shanxi province, impacts of the forest coverage and land-use types on runoff in small watersheds that are similar topographical characteristics were researched in this paper. From the result of analyze, forests have the function of decreasing amount of rain season runoff. Amount and process of runoff in watershed were impacted by forest coverage. By favorable measure of soil preparing, artificial forests have evident function on adjusting runoff and decreasing amount of peak flow of rain season.