ABSTRACT Sequential Pyrolysis Gas Chromatograph is used to study the kinetics of the polystyrene decomposition. All the reactions involved well fit the first-order reaction at pyrolysis temperature ranged from 370-500 °C. The product distribution is described and an independent parallel reactions kinetic model is proposed. The yield of styrene monomer increases obviously with the rising temperature and 90.6%(wt.) is obtained at 500°C. A fluidized-bed reactor is suggested to improve the yield of styrene monomer in industrial practice.