The invention relates to a flame retardant bis[tris(1,3-dichloro-2-propoxy)silicon-acyloxy]ethane compound and a preparation method thereof. The structure of the compound is represented by a formula shown in a drawing. The preparation method comprises the steps of reacting silicon tetrachloride with 1,3-dichloro-2-propanol of a mole which is equal to that of silicon tetrachloride in an organic solvent at the temperature below 25 DEG C, then, dropwise adding glycol of a mole which is 0.5 times that of silicon tetrachloride, heating to the temperature of 65-80 DEG C after completing dripping, and reacting for 7-10 hours; then, dropwise adding 1,3-dichloro-2-propanol of a mole which is 2-3 times that of silicon tetrachloride, and carrying out heat-preservation reaction for 6-10 hours at the temperature of 70-90 DEG C; then, adding an acid binding agent, and carrying out heat preservation for 1 hour while stirring; purifying, thereby obtaining the flame retardant bis[tris(1,3-dichloro-2-propoxy)silicon-acyloxy]ethane. The compound disclosed by the invention has high flame retarding efficacy due to the synergism of silicon and chlorine and is suitable for serving as a flame retardant for materials, such as polyvinyl chloride, polyurethane, epoxy resin, unsaturated resin and the like, and the preparation method is simple and is low in cost, so that the industrial production is facilitated.