While both polybenzoxazine and carbon fiber are attractive due to their excellent mechanical properties, polybenzoxazine suffers from low toughness, and carbon fiber has an inert surface. By incorporating newly designed and synthesized curcumin-based polyurethanes with varying chain lengths into polybenzoxazine (PU1.2 and PU2.0) and the surface of carbon fiber, we were able to introduce variable amounts of hydrogen bonds. Our modified polybenzoxazine exhibited enhanced mechanical properties, such as higher toughness and flexural strength of up to 16.0 kJ/m² and 147 MPa, respectively. In comparison, the flexural strength of our surface-modified carbon fiber reinforced benzoxazine composites was up to 537 MPa. Additionally, the improved mechanical properties of surface-modified carbon fiber reinforced polybenzoxazine are because curcumin-based polyurethanes can significantly improve the interfacial adhesion between the matrix and resin by introducing a soft layer with a high concentration of hydrogen bonds. Our study not only improved the mechanical properties of polybenzoxazine and carbon fibers reinforced polymer composites, but also revealed a novel method for enhancing the mechanical properties of thermosetting resins and interface adhesion of carbon fiber by regulating the hydrogen bonding content.