With the rapid development of advanced equipements， it is of great significance to improve the heat resistance for polymer to expand its application in aerospace field. In this paper， 4，4''-（1， 3-phenoxy） phthalonitrile resin （APN） was modified with SiBCN ceramic precursor to produce high heat resistant material （CPN） and the heat resistance property and mechanism of the modified resin were studied.The results show that when SiBCN mass fraction is 20%， the T_d¹⁰ of the CPN is 608.07 ℃ （N₂）. According to the dynamic mechanical analysis （DMA） results， the glass transition temperature of CPN carbon fiber composites is higher than 500 ℃， which is 100 ℃ higher than that of APN-NH₂carbon fiber composites. When SiBCN mass fraction is 40%， the CPN can maintain the integrity of appearance morphology after 30 min treatment at 900 ℃ under aerobic environment. The ceramic precursors can form Si-O and B-O bonds in the modified resin under high temperature conditions， which significantly improves the heat resistance.