Abstract: A physically-based distributed rainfall-runoff model is developed to simulate the hydrological processes of watershed during rainfall period for considering the spatial variability of terrain,the land use,the soil type and the rainfall distribution. This model discretizes watershed into a number of square elements,and classifies them into hill-slope and channel ones based on the water flow properties.Each hill-slope grid element has model components for interception,infiltration,overland flow and soil water lateral flow,and each channel element has model components of channel flow.The infiltration and excess rainfall on each hillslope element are calculated using the Green-Ampt infiltration equation.Soil lateral flow is based on the Darcy's law and the continuity equation,the overland and channel flows are described by one dimensional kinematic wave approximation to the St Venant equations,and the implicit finite differential scheme is used to solve these equations.This model has the characteristics of simple structure,the process-based equations and the meaningful physical parameters.Most parameters of the model can be derived from the DEM,the digital soil type and the land use data,a few sensitive ones can be determined by the calibration.The model calibration and test are performed in huangtuling watershed(17.9 km²),a sub-basin of Yongjiang river in Zhejiang province,southeastern China,and applied to Jiaokou watershed(259 km²),another sub-basin of Yongjiang river,the results are promising.