Six novel high temperature naphthyl-based low-melting phthalonitrile monomers were prepared using aromatic diphenol (resorcinol, 2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene), 2,6-dichlorobenzonitrile and 4-nitrophthalonitrile, and were polymerized into polymers using 4,4’-diaminodiphenyl ether as initiator. The structures of monomers were characterized by IR, NMR, DSC, and the thermal properties were evaluated by TGA and DMA. The results demonstrate that the melting points of monomers are 90 ℃～116 ℃, and the processing temperature window is about 125 ℃～155 ℃. The initial decomposition temperature (Tid) of the six kinds of polyphthalonitrile resins is higher than 460 ℃ and the limiting oxygen index (LOI) is all greater than 47. The polymers exhibit fine processability, outstanding flame retardancy, excellent thermal stability, and high glass transition temperature (>380 ℃).