A long chain flame retardant (PhN-DOPO) was synthesized from p-aminobenzoic acid, p-hydroxybenzaldehyde and 9,10-dihydro-9-oxa-10-phosphame-10-oxide (DOPO). The results were confirmed by FTIR, 1HNMR and ESI-MS characterization. A series of gradient modified epoxy resins (EP1~EP4) with the addition amount of PhN-DOPO (the addition mass was the percentage of the mass of epoxy resin, the same below) of 0%, 5%, 10% and 15% were prepared. The thermal stability, flame retardancy and bond performance of the modified epoxy resin were investigated by DSC, TGA, LOI, UL-94 and bonding properties. The results showed that the glass transition temperature (Tg) of the modified epoxy resin EP3 increased to 177.2 ℃, the UL-94 test was V-0 grade, and the LOI reached 32.4%, which showed the best flame retardancy and good thermal stability when the PhN-DOPO content was 10%. The bond strength of EP3 was 68.82 N, 6.89 N higher than that of pure epoxy resin (EP1). During the combustion of the modified epoxy resin, PhN-DOPO improved the flame retardancy of the epoxy resin through the synergistic effect of condensed phase and gas phase flame retardancy, and the gas phase flame retardancy of the modified epoxy resin was more significant because the degree of graphitization of the residual carbon was reduced.