A simple and effective modification for carbon fiber (CF) is presented in this work. CF was functionalized with a polydopamine (PDA) layer by pH-induced and oxidative self-polymerization of dopamine through a facile dip-coating procedure. The microstructure and chemical characteristics of the CF surface before and after modification were investigated by SEM, AFM, IR, Raman, XPS and DCA. The results manifested that PDA functionalization could increase the roughness, polarity and wettability of the CF surface, which were advantageous to promote the interaction between CF and the matrix. The interfacial properties of single modified CF (dCF) and pristine CF with resins were measured by micro-droplet method. The interfacial shear strength (IFSS) of single dCF with maleic anhydride grafted PP (MAPP) modified polypropylene (PP) matrix was 284.3% higher than that of PP/CF. Both the dCF and pristine CF were also used to prepare PP composites and their mechanical properties were discussed in detail. The PP/MAPP/dCF composite achieved the combination of excellent flexural and impact properties. The ultimate flexural strength and impact energy increased by 105.0% and 223.0%, respectively. The excellent bulk performance was concluded to be mainly due to the superior interfacial adhesion obtained by covalent reaction and hydrogen bonding between PDA on the CF and MAPP in the PP matrix, which was also confirmed by dynamic mechanical analysis (DMA) and fracture morphology observations.