A flake aluminum powder (f-Al) is prepared by a bi-directional rotation mill method using a spherical aluminum powder (s-Al) as a raw material. Then, these two kinds of aluminum powders are used to prepare ammonium perchlorate-based composite modified double-base (AP-based CMDB) propellants. The properties of two kinds of AP-based CMDB propellants, such as the thermal decomposition performance, mechanical sensitivity, and combustion performance, are comprehensively researched. The results show that the exothermic peak temperature of the f-Al/AP-based CMDB propellant is lower than that of the s-Al/AP-based CMDB propellant. The impact and friction sensitivities of the propellant decrease by 12% and 187% after using f-Al to replace s-Al. In addition, the burning rate of the f-Al/AP-based CMDB propellant is 5.5% higher.