The occurrence states of shale oil are specific and the mechanisms of CO2 injection for enhanced oil recovery (EOR) from shale oil reservoirs are complex. In this study, a crude oil composition model and a rock surface model were established in terms of molecular dynamics simulation based on the crude oil composition and reservoir rock composition of the Bakken shale oil reservoir. Subsequently, the occurrence characteristics of crude oil in shale reservoirs and the competitive adsorption process of CO2-crude oil were simulated using the models, in which the occurrence characteristics of different crude oil components and the effect of crude oil components, rock surface wettability and rock composition on the competitive adsorption of CO2-crude oil were analyzed. The simulation results show that higher oil film concentration and clearer stratification can be promoted by smaller molecular weight, simpler molecular structure and smaller intermolecular force. Intermolecular forces play a dominant role on the motility of oil molecules, thereby affecting the occurrence characteristics of crude oil. The stripping degrees of CO2 to the oil film components of n-C5, n-C12, n-C20, pyridine, phenol, and propanethiol are 55. 29%, 23. 05%, 7. 82%, 31. 36%, 20. 21% and 35. 32%,respectively. The stripping degree of CO2 to crude oil on oil-wet surface is 30. 50%, less than that on water-wet surface. The competitive adsorption effects on different rock surfaces are of quartz (55. 29%), kaolinite (34. 71%) and kerogen (26. 60%) in the order from strong to weak. The interaction between CO2 and shale oil in nanopores can be divided into three stages of CO2 dissolution/ diffusion and crude oil extraction, CO2 and crude oil competitive adsorption, and CO2 storage and oil film pushing and striping. © 2023 University of Petroleum, China. All rights reserved.