Four types of GH₂/LO₂/RP-1 tripropellant injectors are employed to present the mixing characteristics test in this paper. The effects of the internal injector's recess on the mixing characteristics of the swirl coaxial injector with separate fuel injection are studied. The mixing characteristics of each injector are compared with those of the others in the same tripropellant operating condition. The effects of the injectors' configuration on the mixing characteristics are analyzed. The mixing characteristics tests of the single injector and three injectors are presented. The tests results show that the span of the mass flux distribution of the shear coaxial injector is smaller than that of the swirl coaxial injector in the same tripropellant operating condition. The conclusions reached in this paper provide a reference for the optimization design of the tripropellant injectors and the gas/liquid coaxial injectors.