Abstract: Low permeability reservoirs are the main contributors to the discovered and proved reserves in China currently, among which extra-low permeability reservoirs are widely distributed and account for a large proportion of the reserves. However, extra-low permeability reservoirs are characterized by poor physical properties, so it is difficult to enhance single well production by conventional waterflooding method significantly. CO2 flooding can expand oil volume, reduce oil viscosity, lower interfacial tension and capillary resistance and finally improve oil displacement efficiency. In order to develop extra-low permeability reservoirs reasonably and efficiently, based on numerical simulation and orthogonal design methods, CO2 flooding models are established for extra-low permeability reservoirs, and technical and economic evaluations are carried out for the factors influencing CO2 flooding. The analysis indicates that the parameters influencing development effect from high to low are reservoir type, well spacing density and injected CO2 volume. Considering daily well production and internal rate of return and so on, the optimum way to develop extra-low permeability reservoirs is the combination of CO2 flooding in horizontal wells and the corresponding parameters