Abstract: In order to investigate the performance of the hydrogen-rich/oxygen-rich gas-gas injector in the full flow staged combustion(FFSC) engine,the combustion flow fields of the combustors with a shear coaxial injector,a coaxial injector for the oxidizer injector with expansion angle,a coaxial injector for the fuel injector with contraction angle,a coaxial injector for the oxidizer injector with a column in the center and a shear dual-coaxial injector were simulated.The propellant of the injectors was hydrogen-rich gas in temperature of 758 K and oxygen-rich gas in temperature of 676 K.The results of the numerical simulation show that,the shear dual-coaxial injector has the best combustion performance.The results can provide the reliable criterion for the design and experiment of hydrogen-rich/oxygen-rich gas-gas injector.