As an energetic material， octogen（HMX） is widely used in solid propellants. While improving the energy performance of the propellant， it also changes the combustion process of the propellant. To study the effect of HMX content on the ignition， combustion， and agglomeration properties of propellant and its condensed phase combustion products （CCPs）， burning surface photography， laser ignition and collection of the CCPs were used for testing and studying typical AP/HTPB/Al/HMX propellants with HMX contents ranging 0%-10%. Results show that as the HMX content increases from 0 to 10%， the ignition delay time increases from 191 ms to 286 ms， and both the burning rate and pressure exponent of the propellent decreases. The volume average particle size of the CCPs increased from 48.1 μm to 138.3 μm. The propellent with 10% HMX has the highest agglomeration degree on the burning surface， while the propellent with 8% HMX has the highest active aluminum content in the CCPs.