Aluminum based hydrogen storage composite fuel namely Q3 with a content of boron 15% and MgH₂ 15% was prepared by means of chimeric assembly. The powder had a spheroidic morphology. Its theoretical combustion heat was as high as 34.8 MJ·kg^-1. Thermogravimetric Analysis （TGA） was employed to test the oxidation performance of spherical aluminum and Q3. The results indicated that the initial oxidation temperature of Q3 was 430 ℃， which was around 100 ℃ lower than that of spherical aluminum. When the temperature was up to 1000 ℃， the weight of Q3 increased by 60% due to the oxidation， which was higher than that of spherical aluminum （23%）. This result indicated that the aluminum based hydrogen storage composite fuel had a better ignition performance and higher oxidability. The tests of underwater explosion with two RDX based explosive formulas containing 35% metal powder or equivalent Q3 were carried out respectively. The test results showed that for the formula with equivalent Q3， the explosion specific shock wave energy was reduced by 3.0%， the specific bubble energy was increased by 9.5%， and the total explosion energy was increased by 7.6% in contrast to the counterpart formula containing aluminum. The metal hydride and aluminum in aluminum based hydrogen storage composite fuel could effectively improve the energy release efficiency and rate of boron， resulting in increasing the total energy of the explosive in underwater explosion.