To improve the mechanical properties and decrease the mechanical sensitivities of polymer bonded explosives(PBXs), PBXs with 100/0, 95/5, 90/10, 80/20-micrometer/nano-RDX particle gradations were prepared by the solution-water slurry method. Their apparent morphologies were observed with an optical microscope and the mechanical sensitivities, mechanical properties and detonation velocities etc. performances were measured. Results show that the molding powder particles of PBXs with micrometer/nano-RDX particle gradations are smaller and the samples reveal in ball-like particles with regular morphology. PBX prepared with 5% nano-RDX and 95% micrometer-RDX has the best properties, compared with micrometer-RDX based PBX, and the impact sensitivity of PBX with 5% nano-RDX and 95% micrometer-RDX decreases from 44% to 12%, friction sensitivity decreases from 24% to 4%, compression strength increases from 5.55 MPa to 6.57 MPa, tensile strength increases from 0.66 MPa to 0.77 MPa, shear strength enhances from 1.76 MPa to 1.96 MPa, and detonation velocity increases from 8033 m·s^-1 to 8186 m·s^-1.