Abstract: Poly (N-phenylmaleimide–styrene–acrylonitrile–α-methylstyrene) (NSAA) quaternary copolymer was designed and synthesized by micro-emulsion seed polymerization combined with semi continuous feeding method, and the heat resistance modification effect of NSAA on polyvinyl chloride (PVC) resin was also studied. The structure and properties of the synthesized NSAA copolymer were analyzed by nuclear magnetic resonance (H-NMR, ¹³C-NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Research has shown that the synthesized NSAA latex particles exhibit a uniform spherical core-shell structure, while the copolymers exhibit a consistent random molecular structure. The quaternary copolymers have a single glass transition temperature (T_g), and as the N-phenylmaleimide (NPMI) component in the molecular chain increases, the T_g of the copolymers gradually increases, reaching a maximum of 142.6℃. NSAA copolymer exhibits excellent compatibility with PVC resin. When the mass ratio of NSAA/PVC is 30:70, the Vicat softening temperature (VST) of NSAA/PVC composite material is 38.3 ℃ higher than that of pure PVC resin. Mechanical performance testing shows that as the NSAA content increases, the tensile strength of the composite material increases, while the impact strength slightly decreases, but overall degradation is not significant, indicating that NSAA copolymer is an excellent heat resistant modifier for PVC resin and can gradually replace foreign competitors.