Through the analysis of observed data of natural and simulated rainfalls in recent years in Yan’gou watershed,Yan’an City,it is concluded that annually averaged sediment yield decreases by more than 80% in comparison with the case before control. Among the factors causing decreased sediment yield,the contri-bution by rainfall makes up about 30 %,while the contribution by the soil and water conservation measures dominated by vegetation construction,about 70 %. The result proves the importance of vegetation restora-tion in comprehensive watershed managementmeasures.