The simulated rainfall tests have been carried out to approach two stages of raindrop splash and runoff erosion on sheet flow, It was obtained that the main stress of slope surface erosion is sheet flow stress (z=rhsina) where the action of raindrop splash is eliminatecs and the relationship between runoff erosion (Sa) and sheet flow stress is as Ss=92}1.497T1”3 (r=0. 876, a = 0.01).Based on this equation the runoff erosion (Sa) and raindrop erosion (SRe) can be calculaled from the total erosive amount which is caused by the action of raindrop splash .The results show that rain drop erosion(Saa)accounts for more than 700 of total erosion, and the maximum may reach 95%of that .It was indicated that the sediment of sheet flow erosion is mainly caused by raindrop splash .There fore，the authors hold that the lcey'measures to control sheet flow erosion，occurring at the land segment of Less steepness are to reduce or eliminate the raindrop splash,