Abstract: EPDM-g-MAN, synthesized by suspension grafting copolymerization of methyl methacrylate and acrylonitrile onto EPDM, was blended with polyvinylchloride(PVC) resin. The mechanical properties、thermal stability、phase structure and toughening mechanism of the PVC/EPDM-g-MAN blends were studied by TG、SEM and TEM. The results show that: comparing with chlorinated polyethylene(CPE), EPDM-g-MAN had a better toughening effect on PVC resin. TEM and SEM analysis of the blends shows that PVC/EPDM-g-MAN were were partially compatible .When the EPDM content was low, the toughening mechanism of the blends was branch and termination of crack, and then changed into shear yielding and cavition as EPDM-g-MAN increasing.TG and DTG analysis shows that the thermal stability of PVC was improved after being blended with EPDM-g-MAN.