Many parameters were recognized as affecting factors of slope runoff,such as precipitation volume,precipitation intensity and vegetation.Runoff plots were established in a small watershed,Wangdonggou of Changwu County,Shaanxi Province.The method of grey rational degree was applied to analyze the effects of the precipitation and vegetation on slope runoff and erosion by comparing influencing factors.The results indicate precipitation had the highest rational degree with slope runoff and erosion.The parameters contributing to slope runoff in the descending order were rainfall volume,maximum rainfall intensity,rain intensity,and vegetation coverage.The parameters contributing to erosion in the descending order of rational degree were rainfall,rain intensity,maximum rainfall intensity,and vegetation coverage.When the coverage was lower than 25%,runoff volume was similar;when the coverage was over 25%,runoff volume reduced with increasing coverage.When the coverage was lower than 50%,the total erosion decreased rapidly with the increasing coverage.However,the erosion-reducing efficiency of the vegetation significantly decreased when the coverage was higher than 50%.