Foamed non-Fickian diffusion (FNFD) model for a ternary system was proposed for the first time to regress the desorption data obtained by the gravimetric method. Results showed that FNFD model could accurately describe the diffusion behavior of CO 2 and ethanol out of foamed polystyrene (PS) and well predict total solubilities of CO 2 and ethanol in foamed PS. Meanwhile, Sanchez-Lacombe equation of state (S-L EoS) was adopted to calculate the respective solubilities (solubility of CO 2 in PS or solubility of ethanol in PS) and total solubilities of CO 2 and ethanol in PS for CO 2 -ethanol-PS ternary system. Results showed that the total solubility of CO 2 and ethanol obtained from S-L EoS agreed well with values obtained by FNFD model. Furthermore, the respective and total solubilities of CO 2 and ethanol at 313.15, 338.15, and 343.15 K were calculated by S-L EoS. Results indicated that in the dissolving process, ethanol would be accelerated by CO 2 to dissolve into PS, and ethanol would compete with CO 2 to dissolve into PS, simultaneously.