Enhancing the mechanical properties is always an attractive challenge in the research area of energetic materials (EMs). In the present work, 1.5 wt% MN-plasticizers (mononitrotoluene compounds, a mixture of 2-nitrotoluene and 4-nitrotoluene) were applied for reinforcing a molten-energetic-composite (MEC) 2,4,6-trinitrotoluene (TNT)/1,3,5-trinitrohexahydro-1,3,5-triazine (RDX). Brazilian disk testing results show that the tensile modulus of reinforced MEC increases by 26%. In order to explore the reinforcement mechanism, quantum chemistry (QC) and molecular dynamics (MD) simulations were performed to study the structural and physical properties of the reinforced MEC. The basis set superposition error (BSSE) and the interaction energies of TNT, RDX and plasticizers were computed at the MP2/6-311++G** level. Compared with the weak interaction energy between RDX and TNT (−1.586 kJ mol⁻¹), the interaction energies of reinforced MEC increase massively after incorporating MN-plasticizer. The SEM images of fractured surfaces from MECs also reveal that MNs can form layered deposits in TNT and closely surround crystalline RDX due to the presence of strong intermolecular interaction. Besides, MD simulation results further explain that the tensile modulus of (100) TNT and (100) RDX increases when introducing MN plasticizer separately, which agree with the change trends of mechanical properties from the Brazilian disk test. This work provides a new path for studying reinforced energetic composites by combining microscopy, mechanical testing and theoretical simulations.