A kind of polymeric silicone flame retardant charring agent, polydimethyl silicon acid terephthalic diester was synthesized from dichlorodimethylsilane and hydroquinone. The effects of reaction time and reaction temperature on the yield were investigated. The optimum reaction conditions were: n(dichlorodimethylsilane):n(hydroquinone)=1:1, dropping dichlorodimethylsilane to hydroquinone at the temperature of 40℃, keeping the reaction at 70℃ for 7h. The target products would be received after purification, its yield was 96.7%. The structure and flame retardance of the product were characterized by means of FTIR、1H-NMR、TG-DTA and limiting oxygen index technique. The results showed that the product had a good charring flame retardant effect when applied to PBT or PP. And its complex formulation with APP had good synergistic effects.