Boron modified phenolic (BPF) resins with different boron amounts were synthesized with a special synthesis technology. The structure of BPF resin was analyzed by Fourier transform infrared spectra (FTIR) and its curing behavior was analyzed by differential scanning calorimeter (DSC). The results showed that boric acid reacted with the hydroxyl groups in phenolic resin to form a new cross-linked bond such as B-O. At the same time, the heat resistance of BPF resin was improved about 18% with addition of boric acid of 0.8wt%. The obtained BPF had a high curing temperature of 254.6when the boric acid amount was 0.8wt%.