The self-catalyzed novolac phthalonitrile with varying degrees of substitution (NPN60, NPN70 and NPN85) were synthesized by nucleophilic substitution reaction, using novolac resin and 4- nitrophthalic as raw materials. The chemical structure was characterized by FT-IR, ¹H-NMR and ¹³C-NMR. The effects of the degree of substitution on curing, rheological behavior and thermal properties of NPN resins were studied by DSC, rheometer, FT-IR and thermogravimetric analysis. The results show that NPN resin can realize self-catalyzed polymerization. The curing temperature of NPN resin increases and the processing window is broadened with the increase of substitution degree. The cured NPN resins form a thermally stable phthalocyanine structure. The temperature of 5% mass loss (T_d5) of NPN85 cured resin in nitrogen and air is 511.8 ℃ and 506.9 ℃ respectively. After long-term thermal oxidation aging environment simulation at 250~400 ℃ , NPN85 has mass retention rate of 80.6% and thermal oxidation stability.