In order to clarify the solvent effect on the thermal decomposition of explosive, the N-NO2 trigger-bond strengths and ring strains of RDX (cyclotrimethylenetrinitramine) in its H-bonded complexes with solvent molecules (i.e., tetrahydrofuran, acetone, toluene, and benzene), and the activation energies of the intermolecular hydrogen exchanges between the solvent molecules and C3H8O2N4 or CH4O2N2, as the model molecule of RDX, were investigated by the BHandHLYP, B3LYP, MP2(full), and M06-2X methods with the 6-311 + + G(2df,2p) basis set, accompanied by a comparison with the calculations by the integral equation formalism polarized continuum model. The solvent effects ignore the ring strain while strengthening the N-NO2 bond, leading to a possible decreased sensitivity, as is opposite to the experimental results. However, the activation energies are in the order of C3H8O2N4/CH4O2N2∙∙∙acetone < C3H8O2N4/CH4O2N2∙∙∙THF < C3H8O2N4/CH4O2N2∙∙∙toluene < C3H8O2N4/CH4O2N2∙∙∙benzene < C3H8O2N4/CH4O2N2, suggesting that the order of the critical explosion temperatures might be RDX∙∙∙acetone < RDX∙∙∙THF < RDX∙∙∙toluene < RDX∙∙∙benzene < RDX, as is roughly consistent with the experimental results. Therefore, the intermolecular hydrogen exchange with the HONO elimination is a possible mechanism of the solvent effect on the initial thermal decomposition of RDX. The solvent effect on the sensitivity is analyzed by the surface electrostatic potentials.