Timeliness and accuracy of flood forecast can provide important theoretical guidance and basis of decision for flood control and disaster reduction，flood risk assessment，water resources allocation and management，etc.Based on Topmodel and one-dimensional hydrodynamics theory，a set of loose distributed hydrological model for small and medium-sized basins was constructed，choose 40 representative floods，evaluated the simulation accuracy of the model.The results show that the qualified rate of peak-apparent time error absolute value is 97.5%，the qualified rate of relative error is 75%，the qualified rate of efficiency coefficient is 77.5%.The loosely distributed hydrological model constructed in this paper has few parameters，fast calculation speed and strong physical mechanism，which can provide a new idea for the application of distributed hydrological model in real-time flood forecasting.