On the mechanical properties of NC/NG/AP/Al composite modified double-base (CMDB) propellant, the effects of the content of NC, the ratio of solid components granularity and the system of solidifying agents, were studied. The results show that the maximum stress ( σ_m, +20 ℃ and +50 ℃) of the CMDB propellant decreases with the content of NC decreasing, and the maximum elongation ( ε_m, +20 ℃ and +50 ℃) of the propellant reaches the maximum value when the content of NC is 20%. The ratio of solid components granularity affects the mechanical properties of CMDB propellant obviously which reaches the maximum value when the ratio of AP(96.8 μm)∶RDX(44.9 μm)∶Al(10.8 μm) is 1∶1∶1. It is found that for the CMDB propellants with low content of NC, the maximum stress of the propellant can be increased at a certain extent and the maximum elongation of the propellant can be increased obviously when the cross linking agents is added suitably.