To explore the expansion characteristics of multiple wall combustion-gas jets which uniformly distributed along the circumferential direction under high temperature and high pressure in confined liquid working medium, the combustion gas generator and cylindrical filling liquid chamber were designed. The expansion processes of multiple wall jets were recorded by high-speed digital photographic system. The average axial displacements of multiple wall jets at different time were achieved by disposing the expansion sequence diagrams. It shows that the irregular interface induced by the Kelvin-Helmholtz instability exists in the entire jets expansion process. The effects of the number of orifices and the blasting injection pressure on expansion characteristics of multiple wall jets are discussed. The experimental results indicate that, as the number of orifices increase from four to eight, the axial expansion displacements of multiple jets decrease, at t=5 ms, the number of orifices increase from four to six, the axial expansion displacements decrease 8.3 percent, and it decrease 3.1 percent when the number of orifices increase from six to eight. The larger the blasting injection pressure, the greater the axial expansion velocity, the earlier jets get to the top of liquid filling chamber, at t=5 ms, the blasting injection pressure increase from 12 MPa to 20 MPa, the axial expansion velocity increase 20.1 percent, and it increase 19.9 percent when the blasting injection pressure increase from 20 MPa to 28 MPa.