A five-stage cylindrical stepped-wall observation chambers and a cylindrical observation chambers were designed to explore the expansion characteristics of high-temperature high-pressure twin combustion-gas jets in bulk-loaded liquid. The expansion processes of the twin combustion-gas jets in the designed chambers filled with liquid were observed by using a high-speed photographic system. The influences of the different observation chamber boundaries and the conditional parameters were compared. The experimental results show that the cylindrical stepped-wall observation chambers can be more helpful for improving the mixing characteristics of twin gas jets with liquid. And the expansion processes of the twin combustion-gas jets in the three-dimensional filledliquid chambers can be controlled in a certain degree by correctly matching the condition parameters.