Abstract: The weak interfacial bonding property of carbon fiber reinforced polymer composites (CFRPs) significantly constrain their practical application in advanced fields such as aerospace and industrial engineering. Inspired by the bio-adhesion property of mussels in nature, the organic polydopamine (PDA) layer was self-polymerized on the carbon fiber surface as a versatile platform, and different contents of Co(OH)₂ nanosheets were further introduced on its surface via self-assembly process to improve the interfacial bonding between the fiber and epoxy. Meanwhile, a series of tests were conducted to investigate the interfacial and mechanical properties of the composites before and after modification. The experimental results demonstrate that the cobalt hydroxide-polydopamine synergistic interfacial modification significantly enhances the mechanical properties of the composites. Compared with the unmodified composite, the flexural strength, interfacial shear strength, and interlaminar shear strength of the modified composite were increased by 48.1%, 100.5%, and 56.8%, respectively. Briefly, this research provides experimental validation for developing high-performance CFRPs and exhibits promising applications in aircraft and other fields.