The invention belongs to the technical field of gas separation materials, and particularly relates to a mixed matrix membrane for CO2/N2 gas separation, and a preparation method thereof, wherein the mixed matrix membrane is obtained by mixing a mixed solution of PEGMEA and Pebax 1657 and the aqueous solution of a porous organic polymer POP as a film casting solution. According to the present invention, by using Pebax as a polymer membrane material, PEGMEA is added so as to increase the content of the PEO chain segment, reduce the crystallization of the PEO chain segment, and maintain the mechanical properties of the membrane; by adding POP, the characteristics of CO2 philicity and N2 phobicity of the membrane are further improved, and the obtained CO2 gas separation membrane achieves the separation of CO2/N2; and the preparation method is simple and mild, and provides the basis for the large-scale preparation of CO2 gas separation membranes.