Abstract: In coupling model of hydrology and hydrodynamics,the inaccurate calculation of hydrology model is the cause of the discrepancy between the lateral inflow of hydrodynamics and practical case,so the lateral inflow is updated by using the inverse analysis based on the principle of water balance.With water stage and discharge being state variables,the systematic state equation of Kalman filter is set up based on the Saint-Venant equations solved by the four point linear implicit form.Through the inverse analysis,the unbalance of water stage and discharge are put back to the lateral inflow and adjusted,then the updating water-inflow in forecasting period.The inverse analysis method of the interval inflow is applied to the flow calculation for the river section from Cuntan to Wanxian of the Yangtze River,adopting the flood information of construction period with reservoir storing water as high as 135 m and river section from Datong to Zhenjiang with hydrological information of 1998.The forecast of 6-hour lead time proves that the performance of the inverse analysis method is feasible.