In this study, 2-(2-hydroxy-4-acryloyl)-2H-benzotriazole (BTHA), a benzotriazole ultraviolet absorber monomer, was synthesized from 2-(2,4-dihydroxyphenyl)-benzotriazole (BTDP) and acryloyl chloride. The synthesized BTHA was characterized by 1H-NMR, FTIR, and ultraviolet spectroscopy, and grafted onto polyester fabrics by the traditional pad-dry-cure (PDC) process. The effects of monomer concentration and initiator concentration on the UPF values of the grafted PET fabrics were studied. The grafted fabrics were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The breaking strength of the grafted PET fabrics was comparable with the original PET fabrics in warp and weft directions. The UV protection factors improved significantly after grafting. The modified PET fabrics exhibited good durability to washing. The grafting of BTHA onto PET fabrics protected the damage of UV light to PET fabrics and decreased the strength loss of PET fabrics after UVA light exposure.