Abstract: PP-g-malic anhydride (MAH)/styrene (St) was prepared by a twin-monomer solid phase grafting method. The optimum condition was determined by orthogonal experiments with a reaction temperature of 120 ℃, a reaction time of 1 h, a St/MAH molar ratio of 1.2∶1, a MAH/PP mass ratio of 0.14/1, and a BPO/PP mass ratio of 0.02/1. The characterization results of FTIR and NMR spectroscopy indicated that MAH and styrene were successfully grafted into PP by free radical copolymerization. DSC and XRD investigations indicated that PP presented α-form crystals without any changes before and after grafting. However, the crystallinity degree of PP decreased, and its crystallization temperature increased. As a compatibilizer, the incorporation of PP-g-MAH/St enhanced the impact strength of PP compounds.