The distributed hydrological model represented by the Grid Xin'anjiang model was used for flood simulation and forecasting in the Qinhuai River Basin. The spatiotemporal simulation is highly refined in the middle and upper reaches, but its application accuracy is limited in the downstream reaches. In this study, the Qianhancun (Qin) station is used as the node, the grid Xin'anjiang model is used to calculate the runoff in the upstream, the hydrodynamic model is used to simulate the water level of the tidal river section affected by the operation of the gate pump in the downstream, and the K-nearest neighbor (KNN) algorithm and feedback method is adopted to correct the simulation results in real time. After the correction of the KNN method, the coefficient of certainty is 0.718-0.975, which meets the forecast accuracy requirements of Class B.