Rainfall runoff simulation and flood forecasting of large river basins is a complex prediction problem. An integrated hydrometeorological forecast model is developed for flood forecast test of complex river basins. Gridbased quantitative precipitation forecast products of National Meteorological Centre are applied as precipitation of leadtime period, and the Xin′anjiang hydrological model is used for rainfallrunoff process simulation. The MuskingumCunge model, based on diffusion, columbar storage and wedge storage theory, is introduced for channel waterlevel and discharge forecasting. For the test case of the upper reaches of the Lutaizi Station of the Huaihe River in flood season of 2016, the developed hydrometeorological forecast model of complex river basins is applied in flood forecast test. The results show that the developed model can perform well. Compared with no considering the precipitation in leadtime period, the flood forecast leadtime can be increased obviously. The developed model has certain reference significance for flood forecasting over similar basins.