Abstract: Acid (1 - oxo-2 ,6,7 - three oxa-1 - P-bicyclo [2.2.2] octan-4 - yl) methyl ester (PEPB) as carbon agent was Synthesized by Oxygen-4 - (hydroxymethyl) -2, 6, 7 -trioxa - phosphabicyclo [2, 2, 2] octane (PEPA) and benzoyl chloride.The accuracy of structure was proved by FT-IR and 1H-NMR. PEPB and melamine（MA）with ammonium polyphosphate (APP) were mixed as intumescent flame retardants. when the mass ratio of APP,MA and PEPB were 2:1:2 ,the mass fraction was 30%, vertical buming test of the flame-retarded ABS composites reached V-0. The tensile strength and absorbency of composites were 40.15MPa and 1.77%.Compared to the intumescent flame retardants made of APP,MA and PER, the tensile strength increased by 33.4% and absorbency decreased by 84.2%. The char layer microstructure was compact.