Based on sandstone reservoir samples from Songliao Basin, we conducted carbon dioxide displacement experiments on saturated crude oil cores. These experiments were combined with nuclear magnetic resonance and oil component analysis to study the mechanism of carbon dioxide oil recovery. We selected rock samples with varying permeability, including medium, low, ultra-low, and tight permeability in Songliao Basin, to analyze the effect of permeability on carbon dioxide displacement. The displacement experiment was divided into three stages to analyze the effect of injected volume on CO2 displacement. Our research focused on high CO2 injection carbon dioxide flooding of ultra-low and tight permeability rock samples. The mechanism of high CO2 injection flooding of ultra-low permeability and dense reservoirs in Songliao Basin is studied using the method of controlling variables. Experiments show that high CO2 injection flooding can result in good recovery for ultra-low permeability and dense reservoirs. After low injection volume displacement, the average harvesting degree of low-permeability and medium-permeability samples was 30.56%, and that of ultra-low-permeability and dense samples was 26.21%. After high injection displacement, the average recovery degree of low-permeability and medium-permeability samples was 55.92%, while the average recovery degree of ultra-low-permeability and dense samples increased to 67.00%. This indicates that high CO2 injection flooding can effectively improve reservoir recovery, particularly for ultra-low permeability and dense reservoirs. In fact, high injection complete miscible CO2 displacement can achieve a final recovery degree up to 67.49%. Complete miscible displacement can well displace various components of crude oil including heavy components. While there is little difference in the oil family components in different displacement stages, there is still an obvious effect on extracting light components. The peak value of oil components gradually shifts from near C12 in the early stage to near C17 in the late stage. The carbon dioxide extraction leads to the deposition of heavy components on the pore throat surface. The deposition phenomenon is more pronounced in ultra-low permeability and dense reservoirs when injected with low injection volume, but it is weaker in medium and low permeability oil reservoirs. After high CO2 injection flooding, heavy components in ultra-low permeability and dense reservoirs are well recovered, and the final recovery degree of heavy components is similar to that of medium and low permeability oil reservoirs. This indicates that high CO2 injection flooding is more suitable for ultra-low permeability and dense reservoirs. The research results complement the theory of CO2 flooding in ultra-low permeability and dense reservoirs and provide theoretical reference for the subsequent construction of CO2 flooding projects in Songliao Basin.