Using reactive molecular dynamics method with the reactive force field framework, the thermal decomposition of nano-AlH3/TNT and nano-AlH3/CL-20 composites was investigated to develop new high explosives. The binding energies and relaxed densities of the composites show that the compatibility of TNT/AlH3 is better than CL-20/AlH3, which is confirmed by the DFT calculations. The pyrolysis simulations showed that the potential barrier of TNT/AlH3 (1.14 kJ g(-1)) and CL-20/AlH3 (0.72 kJ g(-1)) are smaller than pure TNT (1.99 kJ g(-1)) and pure CL-20 (1.01 kJ g(-1)), respectively. This indicates the catalytic effect of AlH3 nanoparticle on the decomposition of TNT and CL-20. The catalytic effect was confirmed by the DFT calculations of the R-NO2 rupture of TNT and CL-20 molecules on AlH3 surfaces. The slower heating rate (r(h)) of 16 K ps(-1) led to similar evolution results as r(h) = 32 K ps(-1), which implies that the dependence of the simulation results on the heating rate is small. Moreover, TNT/AlH3 and CL-20/AlH3 release 1.07 and 1.97 kJ g(-1) more energies and generate 33.8% and 14.0% more total gas products than pure TNT and CL-20, respectively. Therefore, AlH3 nanoparticles can improve the detonation performance and specific impulse for TNT and CL-20. These are in accord with the effect of AlH3 on nitromethane and ammonium perchlorate/hydroxyl-terminated polybutadiene propellants in the experiments. As a result, the nano-AlH3/TNT and nano-AlH3/CL-20 composites can be promising candidates of new high explosives.