Abstract: Surface rainfall calculation of heavy rainfall process in Dujiangyan during July 8 ~ 11, 2013 are compared and analyzed by use of GIS common method of grid interpolation, inverse distance weighting (IDW) , spline function method (Spline) , Kriging, Co-kriging, Tyson polygon method (Thissen) . And FLoodarea model is used to simulate the flood process of Baisha River Basin. The results indicate that the 5 methods for calculating surface rainfall are restricted by the intensity of rainfall stations and the spatial distribution characteristics of precipitation. In particular the Spline and the Thissenare more sensitive to the distribution of rainfall stations.In the calculation of hourly rainfall, the distribution of sites has greater influence on the Spline.Co-Kriging method can make the FLoodarea's simulation results are better and closer to the true value.The interpolation accuracy of precipitation can be effectively improved and makes the error of Floodarea model simulation smaller by considering the relative influence of topographyin the rainfall calculation under complex terrain conditions.