Abstract: Large-scale hydrological model is usually used to simulate river discharges. However, it does not pay much attention to the simulation of river water depth. Water depth (water level) in rivers, as one of the most important factors, is very crucial in the coupled modeling of river and groundwater. In this paper, the spatial and temporal change of river water depth is fully considered to couple with the groundwater in a spatially distributed hydrological model, WATLAC. The calculation was tested using the Panday and Huyakorn (P&H) tilted V-catchment. The results indicated that model is effective in simulating the spatial and temporal variations of river water depth, and the corresponding water exchange between river and groundwater. Sensitivity simulation also indicated the effects of river bed roughness on water depth and consequently the water exchange volume between river and groundwater. The improved model is applicable to areas where river-groundwater interactions are apparent, and can be used as an effective tool in surface water- groundwater management.