The invention relates to a phthalaznone-containing poly(aryl ether nitrile) end-capped with maleimide and a preparation method thereof. Self-made 4-[4-(4-carboxyl phenoxyl) phenyl) -2-(4-carboxyl phenyl) naphthyridine-1-ketone or derivative thereof and 2, 6-dichlorobenzonitrile are used as polycondensation monomers. Meanwhile, other bisphenol and aromatic bi-halogen monomers can be added, p-aminophenol is used as an end-capping agent, and a solvent, a co-boiling dewatering agent and a catalyst are added for carrying out progressive polymerization reaction and synthesizing a phthalaznone-containing poly(aryl ether nitrile) resin end-capped with amino. On the basis, a phthalaznone-containing poly(aryl ether nitrile) polymer end-capped with amino, maleic anhydride, p-toluenesulfonic acid, a polymerization inhibitor, the solvent and the co-boiling dewatering agent are used as raw materials to prepare a phthalaznone-containing poly(aryl ether nitrile) resin end-capped with maleimide. The poly(aryl ether nitrile) resin can be co-cured with bis-maleimide or an epoxy resin, can be used in the fields of thermostable paint, coatings, adhesives, composite materials and the like and has broad application prospects.