Using glass, polyester, aluminum and carbon fiber as the mechanical modifier of melt-cast explosive RDX/TNT 65/35, the influence of type, content and length on its mechanical property was studied through compressive and tensile experiments. Results show that, the modified effect on compressive strength with polyester fiber is the best, and the compressive strength of the explosive with 0.4% increases to 27.94 MPa. The tensile strength and tensile elongation decreases obviously with decrease of aluminum fiber. The tensile and compressive mechanical properties are degraded when using 0.2% glass fiber than that without fiber. The compressive mechanical performance of RDX/TNT 65/35 increase with the additive amount of glass fiber increase. With 0.01% and 0.05% carbon fiber separately, the tensile mechanical property with 3 mm carbon fiber is better than that with 6 mm carbon fiber, and tensile mechanical properties reach maximum using 0.05% 3 mm carbon fiber.