A hydroxyl group-containing benzoxazine monomer was synthesized as the material of Salicylaldehyde and aminophenol. And then the benzoxazine monomer containing the cyclotriphosphazene structure was prepared by the reaction contioning the activating group cyclotriphosphazene derivatives. The T5% and T10% of the product of Benzoxazine monomer-containing the cyclotriphosphazene is 365℃ and 397℃,respectively. The carbon residue rate of the product at 1000℃ is 48.2%. Compared with the similar benzoxazine monomerwithout three phosphazene ring structure, the heat resistance and flame retardance increase significantly.