In the case of laser direct joining carbon fiber reinforced plastic (CFRP) to A6061 aluminum alloy, the strength of the dissimilar joint is low. The UV grafting of acrylic acid was proposed to modify the CFRP surface before the laser joining process. The result showed that the shear strength of the joint could be enhanced from 5.3 to 30.1MPa when optimized parameters (irradiation distance: 10mm; irradiation time: 30 s) of UV grafting were applied. X-ray photoelectron spectroscopy and scanning electron microscope were applied to study the surface characteristic of grafted CFRP and the strengthening mechanism of the grafting modification. The C=O bond and O-C=O bond on the CFRP increased after the modification with UV grafting. It could be figured out that new chemical bonds, including Al-C and Al-O-C, were produced between Al and the matrix resin of the CFRP and it played a key role in improving the strength of grafted CFRP/A6061 dissimilar joint. Thus, as a high-efficient and effective technique, UV grafting is a promising method to improve the laser joining CFRP to aluminum.