Flood events in River Xitiaoxi Watershed in the upper region of Taihu Basin were simulated by distributed hydrologic modeling system HEC-HMS. The database of hydrology and meteorology in studied region was set up by visual storage system HEC-DSS. The database of the natural attributes of basin was integrated by the technique of GIS Geo-database. The total storm mean area precipitation was calculated by inverse-distance-squared method. SCS Curve Number Loss Model was selected to compute runoff volumes. Kinematic-wave Model was used to model direct runoff and channel flow. Base flow was modeled by Exponential Recession Model and the reservoir model was improved. After calibration and validation, the simulated flow and observed flow fit so good that the efficiency coefficient was more than 0. 8, with error of peak flow within 4% , and error of peak flow time within 2 hours, which illustrated that HEC-HMS may be applicable area in simulating the impacts of land use change on hydrological regimes such as floods.