Abstract: To explore reasonable opening angles of double-stage flag valve,the double-stage flap valve of Jiangxi Ehu pumping station was taken as the research object,and the operating angle of the doublestage flap valve was calculated by theoretical formula to determine the test scheme. The hydraulic loss of the flap valve and the flow state of the water behind the flap valve under different flow conditions and different opening angles of the flap valve were studied,and an optimal opening angle range of the double-stage flap valve was obtained. The research results show that the hydraulic loss is small and its size hardly changes with the increase of flow rate when the opening of the upper section of the doublestage flap valve reaches 46. 00° and the opening of the lower section door reaches 64. 00°． The efficiency decrease caused by the hydraulic loss of the flap valve has been reduced to about 3%,and the flow pattern has been able to develop completely in the culvert. Moreover,with the increase of the opening angle,the impact of the flap valve on the pump device performance and the overall project operation is gradually weakening. Through analysis and research,it is concluded that the optimal opening range of the upper flap valve and the lower flap valve in the double-stage flap valve of Ehu pumping station is 46.00° to 53.00° and 64.00° to 70.00°,respectively. It is consistent with the opening angle of the double-stage flap valve under the operating condition,which can provide reference for the application of double-stage flap valve in the pumping station. By analyzing and comparing from multiple angles,it is concluded that the research method of reasonable opening angle of double-stage flap valve is obtained,which is highly feasible and worthy of popularizing and applying in the research of reasonable opening angle of other types of flap valve.