The development of hybrid bonded fiber-reinforced polymer (HB-FRP) strengthening technology is a breakthrough in the field of structural strengthening and can be used to restrict premature debonding and improve the bearing capacity. Because of the shortage of effective and detailed flexural design methodologies, designers cannot easily apply strengthening technology. Therefore, the design theory of HB-FRP strengthening was studied in this paper. Specifically, the debonding mechanism and failure mode were analyzed, and then the design process for a HB-FRP strengthening system was proposed. The failure criteria that allow concrete crushing or FRP debonding were proposed, which both satisfy the good ductility demand. A model to predict the bearing capacity subjected to different failure modes was built, and good accuracy was obtained according to a comparison with existing tests. The loading characteristics after reinforcement were also verified by numerical analysis, and the occurrence of a single-shear debonding mode after regional debonding is found, which verifies the effectiveness of the fastener design.