Flame charring agent caged dimethicone double cage phosphate were synthesized from 1-oxy phospha-4- (hydroxymethyl)-2, 6, 7- trioxabicyclo [2. 2. 2] octane (PEPA) and dimethyldichlorosilane, it was dimethyl silicate di{1-oxy phospha- 2, 6, 7-trioxabicyclo[2. 2. 2]octane -(4)- methyl} ester (DSDE). The effects of different solvent, eaction temperature and amount ratio of substance on product yield was discussed, the optimal conditions were selected as follows PEPA and dimethyldichlorosilane in molar ratios 2.16:1, the yield was 92.6%. The structure and properties of flame retardant products was characterized by using FTIR, 1H-NMR, elemental analysis, TG-DTA analysis and limiting oxygen index techniques. Experiments showed the product had a good char and thermal stability.