Abstract: Experimental investigation on flowrate characteristics of two different types of GH2/GO2 injectors at different back pressure conditions were used for hot fire test.The effect of the fuel injector on oxidizer injector and the effect of pressure drop on the flowrate characteristics were investigated.The results show that the discharge coefficient of oxidizer injector is bigger than the oxidizer working alone when the oxidizer injector and the fuel injector are simultaneously working,as the back pressure changed from 0.2 MPa to 4 MPa.The discharge coefficient of the oxidizer injector and the fuel injector becomes bigger with the increase of pressure drop,but the trend becomes slower.The results presented in this paper may provide valuable reference for the design and improvement of the gas-gas injector.