Atomic simulation was applied to investigate the interface interactions and mechanical properties of beta-octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX)-based polymer-bonded explosive (PBX) with Estane 5703. The interface structure of HMX (100) crystal surface with Estane 5703 was analyzed using pair correlation function (PCF), and the interfacial binding energies between them were calculated. It is shown that there exist hydrogen bonds and electrostatic interactions on the interface. By calculating and comparing the bonds lengths and distributions for possible initial bonds fractured in detonation, it is known that the interactions do not affect the stability of the PBX. Moreover, the elastic constants for HMX and the HMX-based PBX were computed using static elastic constants analysis method, and the engineering moduli and Poisson ratios were derived by Reuss average. Based on the value of Cauchy pressure, it is indicated that the ductibility of crystalline HMX can be effectively improved by blending the polymer in small amount. The relevancy to shockwave stability for this PBX in detonation was discussed finally.