Abstract: The kinetics of free radical bulk polymerization of styrene using tertbutylperoxy-2-ethylhexyl carbonate (T117) as initiator was studied. The effect of initiator concentration, temperature and ethylbenzene mass fraction on the polymerization rate and molecular weight of polystyrene were investigated. Results showed that when the temperature was 117 °C, the reaction order of initiator concentration was 0.42, the reaction apparent activation energy was 54.8 kJ/mol, and the reaction order of monomer concentration was 1. The molecular weight of PS decreased by about 30%, 20% and 15% with the increasing of the initiator concentration, temperature and ethylbenzene mass fraction, respectively. The initiator concentration was the most effective factor.