N-phenylmaleimide terpolymer manufactured by Yangchen Tech is obtained by emulsion polymerization of N-phenylmaleimide monomer and other monomers. The copolymer has a uniform glass transition temperature and excellent heat resistance stability, and has good compatibility with PVC and other resins. It is a very effective and economical heat resistant modifier for PVC and other resins. It can not only significantly improve the temperature resistance of PVC resin, but also improve its processing performance and Hardness, which has effective modification effects for PVC resin.