Abstract: Through the method of numerical simulation and experiment,investigation was conducted on the shear coaxial injector which uses the gaseous oxygen and hydrogen as propellants.The effects of oxidizer post pattern and wall thickness on characteristic efficiency were discussed.The results show that a small scale recirculation zone is produced near the oxidizer post tip,which serves as a flame holder.The radial velocity generated in flared oxidizer post interferes the recirculation zone,making the characteristic efficiency relatively low,while the straight oxidizer post is beneficial to the flame stability,thus achieving a higher characteristic efficiency,and the wall thickness of oxidizer post has no significant influence on characteristic efficiency.