Abstract: In order to better understand the spray combustion process and the phenomenon of pressure oscillation in regenerative liquid propellant guns (RLPGs), the multiphase multidimensional mathematical model is adopted to describe the flow process in the chamber of an RLPG. The gas filed is described by Euler system and the Lagrange method is used to describe the droplets movement. The droplet combustion is governed by a pressure-dependent burning rate. A spray model is developed based on the surface wave breakup theory and linear stability analysis for the high annular jets in RLPGs. The MacCormack method is used to calculate the gas control equations. It is shown that the numerical results are consistent with the experiment data well. The high-frequency combustion instability occurs in the combustion chamber. The dominant mode of the pressure oscillation is the second radial mode. The movement of projectile dominates the modality of the gas field.