In order to investigate the resistance characteristics of flap gate, the experimental and numerical simulation studies of resistance loss of flap gate were performed. Outlet circulation of the pump has great influence on resistance loss of flap gate, so the resistance loss and the square value of flow do not show the proportional relationship. In the conditions of the same flow, efficiency decreased value of pump system was negative correlated with the open angle of flap gate. On the basis of numerical simulation, flow patterns of the outlet were analyzed with and without flap gate under designed operating condition. The resistance loss of flap gate was predicted. A good agreement was achieved between the predicted data and the experimental data under designed operating condition.