Abstract: In order to preserve the excellent dielectric properties of polyphenylene oxide resin while improving its solvent resistance and thermal stability, and expand its application in the field of high-frequency and high-speed copper clad laminates, this paper synthesized a polyphenylene oxide type phthalonitrile resin (PPOCN) through nucleophilic substitution of 4-nitrophthalonitrile using K₂CO₃ as a binding agent. A comprehensive analysis was conducted on the structure, curing behavior, heat resistance, and processing performance of the resin through FTIR, DSC, TGA, and rheological analysis. The various properties of the composite material were evaluated through dielectric analyzer, dynamic thermomechanical analysis, and mechanical performance testing. The results show that PPOCN has crosslinking reaction activity, and the glass transition temperature (T_g) of the cured product is 295℃, and the 5wt% thermal weight loss temperature (T_d5%) is 419.3℃. Compared with the raw material of polyphenylene oxide, the thermal stability of PPOCN is significantly improved. The fiber reinforced composite material prepared with PPOCN as the matrix resin and diaminodiphenylmethane (DDM) as the curing agent has excellent mechanical and dielectric properties, with a bending strength of 863.9 MPa, interlayer shear strength of 68.6 MPa, dielectric constant of 3.15 at 1 GHz frequency, and loss tangent of 0.003. PPOCN retains the excellent dielectric properties of polyphenylene oxide resin while also possessing excellent mechanical and thermal properties.