Foams in pores affect the sweep range and oil displacement efficiency for low-permeability reservoir. In this paper, regular porous media with different coordination numbers are constructed to study how the parameters of microscopic pore structure affect foam flooding, and to identify the relationship between foam flooding efficiency and pore size. A two-dimensional microscopic pore structure model is established by computed tomography (CT) and the Imagej software. The sweep range and oil displacement efficiency of foam flooding are compared with that of water flooding. The results show that porous media with low coordination numbers can lead to higher foam flooding efficiency. When the pore size of porous media with a coordination number of 3 is 1 μm, the oil displacement effect is the best. Compared with water, foam can significantly improve oil displacement efficiency. Foam can block the dominant channel and drive out the residual oil in the narrow pore throat with higher efficiency. When the gas-liquid ratio of the foam is 3:1, the residual oil saturation is the lowest, and the flooding effect is the best. The higher contact angle of the wetting wall can produce better efficiency of foam flooding. When the wetting angle is 45°, the oil displacement effect is the best. When the injection rate is 0.5 m/s, the oil displacement effect is the best, but when the injection rate reaches 5 m/s, the residual oil saturation is the smallest. When the coordination number is 4, the oil displacement effect is the best.