Foaming of polystyrene (PS)/ supercritical dioxide system was studied in a batch process in order to achieve a better understanding of supercritical CO2 diffusion mechanism in polymer and foaming condition. In this study, PS sample was treated with CO2 at 5-30 MPa and 40-160°C, soaking times was about 30-120min.Using gravimetric method, the solubility of CO2 in PS was obtained. The study datum shows that the solubility of CO2 in PS increases with increment of pressures, but decreases with the increment of temperature. The sorbed amount of CO2 is from 0.02 % (7MPa,160°C) to 0.11%(30MPa,40°C).The relation of glass transition temperature, volume expansion ratio, cells density of foaming with pressure and temperature also was discussed individually. The glass transition temperature of PS swelled with CO2 is 80°C-95°C, which is lower than the glass transition temperature of pure PS by 10°C-25°C. The cell density increases as the pressure increase, and it decrease as the temperature increase.