As a composite material composed of fillers and matrix， the damage of hydroxylated polybutadiene （HTPB） propellant mainly involves particle breakage， matrix fracture， and debonding of the bonding interface layer. To further explore its structural damage and mechanical performance evolution under external loading， a combination of micro CT， high-speed CCD camera， and all atom molecular dynamics simulation was used to analyze the multi-scale damage of the propellant under in-situ loading. The results indicate that the typical damage process of the propellant begins with the failure of the bonding interface layer， extends to the growth of debonding pores， evolves through the merging of pores， accelerates the collection of local large deformations， and terminates at the fracture of the matrix. Meanwhile， the interface binding energy and stress concentration degree cause the large ammonium perchlorate （AP） particles to debond first， and the porosity and strain exhibit an exponential function relationship. Furthermore， the traction separation curve of the micro interface layer conforms to an exponential cohesive force model， where the initiation and expansion of micro voids disrupt their cohesion， while the molecular spacing affects the evolution of stress.