The invention relates to a tris(dichloropropyl) tribromophenoxy chloropropyl silicate compound which is a silicon-halogen synergistic fire retardant, and a preparation method of the compound. The compound has a structure shown in a formula described in the specification; and in the formula, OC3H5Cl2 is OCH2CHClCH2Cl or OCH (CH2Cl) 2. The preparation method of the compound comprises the following steps: reacting tribromophenyl glycidyl ether and silicon tetrachloride according to the same molar ratio in an organic solvent for 4-6h at 60-80 DEG C; then dropwise adding dichloropropanol according to a certain molar ratio, reacting for 4-8h at 50-100 DEG C; and finally purifying to obtain faint yellow liquid which is the tris(dichloropropyl) tribromophenoxy chloropropyl silicate. The compound is applicable to fire retardants for polyvinyl chloride, polyurethane, epoxy resin, unsaturated resin and other materials; and the production process is simple, low in equipment investment and cost, and suitable for industrial production.