Abstract: In order to improve the external load-bearing capacity of solid rocket motor (SRM), the failure mechanism of the composite case structure was studied, and the form of improved structure for composite case structure was put forward.The composite case structure was improved by increasing axial stiffness and lateral bending stiffness of the exterior layer.The axial deformations of interior and exterior layers were in concordance, and the axial load-bearing capacity distribution of exterior to interior layers was improved.The load-bearing capacity of the improved composite case structure was largely increased by about 124% and the structural mass was only increased by less than 10%.Results indicate that the stiffness matching design of the lap-joint interior and exterior layers is the key factor that affects the load-bearing capacity of the composite case structure of SRM.The composite case structure of SRM has the load-bearing capacity well only on condition of coordination of the stiffness match and deformation in lap-joint interior and exterior layers.