To improve the comprehensive performance of polymer bonded explosives(PBXs), low sensitivity nano-HMX and micrometer HMX were applied to PBX by particle gradation. Four molding powders were prepared by solution-water slurry method and pressed into explosive cylinders. The surface microstructures of JO-1, JO-2, JO-3 and JO-4 sampls (coarse/micrometer/nano-HMX mass ratios with 100/0/0, 60/35/5, 60/30/10 and 60/25/15, respectively) were observed and the component contents, impact sensitivities, friction sensitivities, thermal decomposition characteristics, compression properties and detonation velocities were measured. Results show that JO-3 sample has the best properties. Compared to the JO-1 sample with single coarse HMX(d₅₀=100 μm), JO-3 sample has the smoother surface, and the impact sensitivity is reduced by 38.3%, the friction sensitivity is reduced by 22.7%, the self-ignition temperature is increased by 5.17 ℃, the compression strength is enhanced by 46%, and the detonation velocity is increased by 55 m·s^-1. The HMX based PBX comprehensive performance is improved significantly.