Novel host–guest/multicomponent energetic materials can be obtained by embedding hydrogen- or nitrogen-containing oxidizing small molecules between the molecules of high-energy explosives, which can improve their explosive energy. To better understand the mechanism of oxidizing small molecules in the reaction and improve the energy, ReaxFF-lg reactive molecular dynamics simulations were performed to investigate the thermal decomposition reaction at different temperatures of the CL-20/H2O2 solvate formed by embedding H2O2 in the cavity of CL-20. We propose an analytical method to investigate the mechanism of H2O2 in the CL-20 reaction by tracing the interactions between the H and O atoms of H2O2 and the C, H, N, and O atoms of CL-20. During thermal decomposition of CL-20/H2O2, CL-20 and H2O2 first separately decompose, and then, the decomposition products react. The H atoms, O atoms, and hydroxyl (HO) groups generated by H2O2 decomposition connect with the O atoms of nitro groups, leading to N–O bond cleav...