Aiming at the problem that the unstable combustion caused by the abnormal pressure fluctuation of the combustion chamber during the launch process can produce huge chamber pressure which can cause damage to the launch equipment, the influencing factors were studied. The influence of projectile mass, chamber volume, ignition diameter and ignition position on pressure fluctuation was analyzed by means of simulation and experiment. The results show that the amplitude of pressure fluctuation can be reduced by reasonable design of launch conditions, which provides a design basis for the safety of hydrogen and oxygen launch.