In order to study the effects of phases of HMX on the nitramine propellants,the combustion performance and mechanical properties of nitramine propellants containing α-HMX and β-HMX were tested by closed combustion bomb and mechanical properties tester. Results show that the propellant with α-HMX is easy to be ignited and its gas generation brisance and combustion rate is lower than that with β-HMX,and the burning rate pressure exponent of the propellant with α-HMX is 0.1 higher than that with β-HMX and mechanical properties of the propellant with α-HMX is worse. In addition,when loading density is 0.12 g·cm^-3, the two burning rate pressure exponents are larger than 1,and when loading density is 0.20 g·cm^-3, the two burning rate pressure exponents reach the level of less than 1.