SWAT（soil and water assessment tool）,which is based on physical mechanisms,is a distributedhydrological model developed to simulate and predict runoff in different underlying surfaces accurately.Thepurpose of this study is to simulate the monthly runoff from Yangou Watershed in the loess hilly area from2002to 2008by using SWAT model.Results indicated that the correlation coefficients in the period of calibration and validation were 0.96and 0.98with the Nash-Sutcliffe′s coefficient being 0.89and 0.76,respectively.The precision of SWAT simulation is higher than the evaluating criterion（Ens>0.5,r2>0.6）,whichdemonstrates that SWAT is applicable to simulate the runoff from Yangou Watershed and practical in floodmonitoring and forecasting in the loess hilly area.