Abstract: The injection of multiple high-pressure combustion gas jets which is developed by the combustion of powder in a cylindrical water-filled chamber is numerically studied. The Reynolds average Navier-Stokes equations and the k-ε realizable turbulent model are adopted to describe the expansion of a single central Taylor cavity and several lateral Taylor cavities in this limited water environment. The effects of the number of lateral orifices on the gas expansion are discussed. The numerical results show that, when the number of lateral orifices decreases, the shape of Taylor cavities on the section in axial direction has no significant change, but the convergence of adjacent lateral Taylor cavities appears later and the time of Taylor cavities to fill the chamber increases. With a decreasing number of lateral orifices, the static pressure in Taylor cavity tends to be stable and the average total pressure on the section in radial direction decreases.