Tribromophenol sodium was reacted with epichlorohydrin to generate tribromophenyl epoxy propyl ether, then tribromophenyl epoxy propyl ether was reacted with silicon tetrachloride to generate intermediate product tribromophenoxy chloropropoxy silicon trichloride, the intermediate product was further reacted with ethylene oxide, to generate chlorine-bromine silicate ester flame retardants. The effect of reaction temperature, time and amount ratio of substance on the reaction yield was discussed. The optimal conditions for preparation were selected as follows: n(tribromophenyl epoxy propyl ether): n(silicon tetrachloride): n(ethylene oxide) was 1:1:3.2, reaction time was 4h at 50℃. The percentage of the reaction yield could reach 98.6%. The molecular structures of the product and its flame retardant properties were characterized by means of FTIR, 1H-NMR and LOI technique. Applied Research showed that the flame retardants had good flame retardant plasticizer for PVC and other materials.