The interface in carbon fiber (CF)-reinforced polymer composites plays an important role in determining the mechanical properties of composites. In order to improve the interfacial adhesion between the carbon fiber and resin matrix, we presented a facile and rapid method for grafting nano-sized titanium dioxide (nano-TiO2) onto the CF surface by means of thiol-ene click chemistry under UV irradiation. Experimental results demonstrate that the chemical bonds are formed between the CF and nano-TiO2. The introduction of nano-TiO2 significantly enhances the surface energy of fiber and increases the wettability and mechanical interlocking between fiber and resin, resulting in a significant increase in the interfacial properties of composites. Compared to the raw CF/epoxy composites, the composites reinforced by the CF grafted with nano-TiO2 show an improvement of 78% in the interfacial shear strength. Moreover, the results of the mechanical properties tests reveal that the flexural strength and tensile strength of composites increase by 32.3 and 39.6% after grafting with nano-TiO2.