Abstract: This study develops a semi-loose coupling hydrodynamic model integrating the HEC-RAS model and MODFLOW model for quantitative analysis of the water balance in a river-groundwater system, and applies it in a case study of the surrounding area of the lower Lihe River impacted by the mainstream water level. This coupling model adopts two transfer variables: the range of variations in river water level and the volume exchange between river water and groundwater, and reduces flow residual of the system by adjusting its water balance using the Picard iteration, so that bidirectional parameter transmission between the two models and two-way coupling are successfully achieved. Application of the model to calculations of the water balance in the case study reveals that before the water level elevation, most of the water supply in the study area came from rainfall infiltration recharge while the main water discharge was phreatic evaporation. The uplift in water level increased seepage recharge and reduced groundwater discharge, but it produced no impact on the recharge-discharge relation between river and groundwater. Thus, this relation is still dominated by the groundwater discharge to the river, exactly the same as in the previous condition.