In order to choose a main explosive of underwater explosives, analyze the underwater explosion energy output characteristics of RDX and HMX. Separately use RDX and HMX as main explosives, produce R-RDX and R-HMX which are both non TNT melt-cast explosives. Underwater experiment was taken in a diameter of 85 m pool, the underwater explosion pressure and the pulse cycle was measured and shock wave and bubble energy was calculated. Result show that, within 4-6m, the shock wave and bubble energy of RDX based explosive was 1.18 MJ/kg and 4.00 MJ/kg, and HMX based explosive was 1.19 MJ/kg and 4.01 MJ/kg. Compared with RDX, HMX has no energy advantage in underwater explosion in non TNT melt-cast explosive.