Abstract: Surface modification of carbon fiber is the primary method for enhancing the interface bonding strength of carbon fiber/epoxy resin composite (CFs/EP). The unique surface morphology can effectively prevent stress concentration and enhance the comprehensive mechanical properties of the composite. A flower-shaped MgO was synthesized on the surface of carbon fibers rapidly and efficiently using a microwave-assisted method, and its impact on the mechanical properties of CFs/EP composites was investigated. It was found that the flower-like MgO increased the roughness of carbon fiber surface markedly. So irregular interface between carbon fiber and EP matrix formed. As a result, the mechanical interlocking force between carbon fiber and EP matrix was enhanced significantly. This multiscale boundary morphology could increase the crack propagation path. Thereby, more energy could be consumed and the failure of CFs/EP composites caused by stress concentration could be alleviated effectively. Compared to unmodified CFs/EP composite, MgO-modified CFs/EP composite exhibited a 15.2%, 21.8%, and 14.3% increase in tensile strength, bending strength and impact strength, respectively. Therefore, MgO-modified carbon fiber improved the strength and toughness of carbon fibers significantly. The research provides technique support for the wider application of carbon fibers in polymer composite. Meanwhile, it extends broader ideas for fibers with much more unique surface morphologies in strengthening polymer composite.