The Star macro-initiator of octakis(2-bromo-2-methylpropionoxypropyl dimethyl- siloxysilsesquioxane(OBPS) was synthesized via hydrosilylation and esterification with octakis(dimethylsiloxy)silsesquioxane(Q8M8H), allyl alcohol, and 2-bromo-2-methylpropionyl bromide. The structure of OBPS was characterized by FTIR, 1H-NMR, 29Si-NMR and GPC methods. The influence of solvent, temperature and reaction time on the product structure and yields was discussed. The optimal experiment conditions were: solvent THF, 0℃ for 3h and then room temperature for 20h. The yield was 85.0%. OBPS can be used as the macro-initiator in atom transfer radical polymerization to synthesize star polymers.