In this article, we study the dewetting phenomenon of a polymer and carbon dioxide (CO2) mixture on a planar surface by combining density functional theory and the string method. It is found that dewetting is a first-order discontinuous phase transition. When the pressure is lower than the completely dewetting pressure (P-d), CO2 stabilizes the polymer films. The density fluctuation of the polymer decreases significantly with the inclusion of CO2. When the pressure is above P-d, the polymer film is depleted far away from the surface, leaving a thick layer of pure CO2 in the region near the surface. P-d is proportional to the surface energy strength. The CO2 molecules enhance the density fluctuation of the polymer during the dewetting process. The polymer-rich phase at the triple point dewets to a CO2-rich vapor film, as the CO2-rich liquid film near the surface is metastable. These results have promising application in the industry of fabricating polymer films and antifouling polymers on attractive surfaces.