In order to better apply the Grid-Xin’anjiang(Grid-XAJ)model in the flood simulation and forecasting in areas affected by reservoir discharge, the effect of reservoir discharge on the model confluence calculation was compared between the segmented Muskingum(MK) method, grid-based MK method and grid-based Muskingum-Cunge-Todini (MCT) method, based on the real geographical location of the reservoir in the Hengpaitou Watershed. The results show that the flood peak simulation of the three schemes is good, and the average pass rate of all the floods in the periodic and verification period of each scheme rate is 100%. The average pass rate of runoff depth in the grid-based MK method and segmented MK method is 76.9%, which is lower than that of the grid-based MCT method, 84.6%. Compared with the segmented MK method, grid-based MCT method and grid-based MK method can reflect the influence of upstream reservoir discharge on the spatial and temporal distribution of discharge in the catchment process. Grid-based MCT method further considers the real situation of the underlying river channel on the basis of grid-based MK method. In general,grid-based MCT method has strong adaptability and reliability for flood forecasting in basins affected by reservoir drainage.