The present invention relates to an oil extraction efficiency improving chemical additive for oil fields, and a preparation method thereof, particularly to a profile control foaming agent soluble in supercritical carbon dioxide, and a preparation method thereof, wherein the structure of the surfactant is characterized in that carbon dioxide-philic branched epoxy alkyl, an ester group and a carboxylate characteristic group are introduced into the hydrophobic chain, such that the surfactant has characteristics of good carbon dioxide affinity and good hydrophilicity. According to the present invention, the alkyl alcohol is adopted as the starting agent to initiate the epoxy alkane polymerization, and the carboxylation reaction is performed to prepare the final product; and the surfactant has advantages of mature and easy-operating synthetic route, and high solubility in supercritical carbon dioxide.