In order to study the combustion characteristics and atmosphere pressure flame structures of ACP-containing HTPB propellants, the high-pressure burning rate test system of solid propellant was employed to test burning rate over the pressure range 3-29 MPa. The condensed combustion products of propellants at 3, 10 and 20 MPa were collected, their morphology, particle size distribution, active aluminum content and alumina crystal form were analyzed. High-speed photography system was employed to monitor the combustion process of ACP on the combustion flame structure and the burning surface. The combustion surface and quenched surface were obtained for morphology and composition analysis. Results indicate that the addition of ACP effectively increases the burning rate, the ACP addition of 5% increases the burning rate by 84.8 % at 29 MPa, and unstable combustion pressure zone occurs at 9-11 MPa. The active aluminum content of combustion products is 13%-16% at 3 MPa. At atmosphere pressure, large-sized particles with 100 μm in diameter are brought into the gas phase from the combustion surface by the combustion gas. The molten aluminum particles have no obvious agglomeration on the burning surface. The addition of ACP increases the irregularity of the combustion surface.