A microcellular combustible ordnance material composed of 70% RDX (cyclotrimethylene trinitramine) and 30% PMMA (poly methyl methacrylate) was fabricated using the solvent method and foamed by supercritical CO2 as foaming agent. This material has a number of advantages and many find potential application in weaponry. In this paper, vented bomb tests were conducted on the porous materials to gain a qualitative understanding of how the material is burning in a gun environment. The extinguish process showed that the microcellular combustible material followed the in-depth combustion mode, i.e. the combustion products infiltrated through inner pores as well as ignited the inner pore surface. With increasing burning degree, the depth and perforation size of infiltration zone increased. Closed bomb tests were also conducted to investigate the influences of test conditions on the burning behaviors. The results showed that when the ignition pressure was increased from 10.98MPa to 15.0MPa, the burning time was shortened, but the mass burning rate and vivacity did not change obviously. Mass burn rates at different loading densities indicated that while the pressure in closed vessel is high enough (p40MPa), hot combustion gases were driven into the inner pores and convectively ignited the inner pores. The closed bomb results conducted at high and low temperature showed no abnormal burning behavior at low and high temperature can be observed.