Parameter calibration is an important process for model applications. The accuracies for model simulations are usually highly related to the results of parameter calibrations. This study aims to investigates the possibility of using HEC-HMS (U.S. Army Corps of Engineering Center) to investigate the rainfall-runoff of the Lanyang River. The basin model for the watershed is constructed by using the ArcView software package based on the Digital Elevation Model (DEM) for the area. Rainfall and flow data are obtained from the existing 9 precipitation gages and 5 stage gages, respectively. By utilizing Optimization Tool in HEC-HMS, the optimal parameter set for the Langyang River is obtained.