In order to increase the hydrophility of polypropylene (PP), acrylic acid(AA) was grafted on to the surface of PP powder by means of photo-initiated solid phase grafting reaction with the photo-sensitizer of benzophenone in the reaction equipment of UV polymerization. The effects of AA content, amount of initiator, irradiation time, and swelling time on grafting degree were systematically studied. The result shows that in the processing of AA grafting reaction the highest value, 5.2%, of grafting degree can be obtained when the content of AA is 1 mL, amount of initiator is 0.15 g, irradiation time is 30 min and swelling time is 12 h. With the grafted sample the dye ability is 43.4%, tensile strength drops 1.37 MPa of the grafted PP, but breaking extension degree increases to 396.3% from 358.3%. This indicates that the effect of moderate grafting of acrylic acid on the mechanical performance of PP is not obvious.