In order to investigate the combustion flow field of gas/gas injector in full-flow staged combustion cycle engine, the flowing combustion processes of different velocity ratios between fuels and oxidants were numerically simulated by solving the Navier-Stokes equations. Simulation results which agree well with the experimental results show that: the combustion efficiency increases and the combustion flame surface advances along with the increase of velocity ratio; if the length of the engine is restricted, the effective combustion can be achieved by increasing the velocity ratio appropriately.