Addressing the issue of insufficient flood forecasting accuracy during the Meiyu period (June 18-28) in the Fenshuijiang River Basin, this paper investigates the practical application and improvement method of coupled "Xin'anjiang + Muskingum" hydrological model. Based on the observed rainfall and reservoir operation data, the evaluation of forecasting precision for peak discharge, runoff depth, and time-to-peak was conducted through relative error analysis. The accuracy of the model was verified by comparing the measured values with the predicted values in combination with the deterministic coefficient (D_DC). The forecast effect was optimized by correcting the runoff yield and concentration parameters of the Xin 'anjiang model and the flow routing parameters of the Muskingum model. The results show that after parameter adjustment, the peak discharge relative error is below 15%, runoff depth error is low 40%, time-to-peak deviation is within 2 hours, and D_DC values exceeds 0.85; However, there is still a lag in the forecast during the concentrated period of heavy rainfall. The correction coupled model significantly enhances flood forecasting accuracy during the Meiyu season, offering reliable support for reservoir operation decisions. In the future, it is necessary to further optimize the dynamic coupling mechanism between the input of rainfall spatio-temporal distribution and the parameters of river routing parameters.