In view of the development of dominant seepage channels and the deterioration of displacement effect after water flooding in highly heterogeneous multi-layer sandstone reservoirs, taking typical reservoirs in Jidong Oilfield as an example, the research and application of carbon dioxide flooding technology were carried out. The mechanism of CO2 flooding was studied by online NMR, thin tube experiment, oil–gas phase permeability experiment, and long core displacement experiment. The results show that CO2 can enter the pore throat that cannot be displaced by water flooding, and the lower limit of effective displacement can be as low as 0.01 μm pore throat radius and 0.1 mD permeability reservoir. At the same time, with the increase of injection pressure, the oil displacement efficiency increases significantly, and the oil recovery can be increased by more than 30% points compared with water flooding. It is feasible to carry out CO2 flooding in strongly heterogeneous sandstone reservoirs. However, the stronger the reservoir heterogeneity, the more likely CO2 gas channeling, affecting the sweep coefficient. Both field practice and numerical simulation show that gravity flooding can effectively slow down the occurrence of gas channeling, which is the key to achieving the effect of gas flooding. The formation dip Angle is greater than 35°, positive rhythm reservoir, permeability ratio of vertical to horizontal > 0.8, and formation crude oil viscosity is less than 5 mpa s, injection rate is less than 0.06 HCPV/a, gravity flooding effect is more obvious, gas flooding effect is better.