Abstract: With benzoyl peroxide (BPO) as initiator, the surface of polypropylene (PP) fibers was modified with acrylic acid by two step-chemical grafting methods. The effects of initiation temperature, concentration of BPO, grafting temperature, grafting time and concentration of AA on the grafting degree of PP fibers were studied with orthogonal analysis method, and the interfacial bonding between cement matrix and PP fibers before and after modification was evaluated. The results show that the influence of above factors on grafting degree of PP fibers in order is initiation temperature>concentration of BPO> grafting time > grafting temperature > concentration of AA. The optimum reaction conditions are as follows: initiation temperature is 90℃, concentration of BPO 4.50×10^-2 mol/L, grafting time 60 min, grafting temperature 75℃ and concentration of AA 1.4 mol/L. Under this condition, the grafting degree of PP fibers is 13.12%. Though two step-chemical grafting modifications, the surface hydrophilicity and roughness of PP fibers are increased, so that the interfacial bonding between PP fibers and cement matrix is enhanced. When the volume fraction of modified PP fibers is 0.05%, the cracking-resistance ratio of PP fibers reinforced cement mortar increase by 26.6%, which indicate its plastic shrinkage cracking resistance is significantly enhanced.