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