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The effective displacement of the shale oil from organic nanopores plays a significant role in development of the shale oil reservoirs. In order to deeply understand the microscopic displacement mechanism of alkane of shale oil by CO₂ in organic nanopores, microscopic pore model of organic matter and molecular model of CO₂ and n-dodecane were established to investigate the influences of key parameters on the displacement process by using the Monte Carlo and molecular dynamics simulation method. The instantaneous adsorption of molecules demonstrates that the displacement of n-dodecane and the adsorption of CO₂ are proportional to the increase of the injection pressure of CO₂ as well as the pore size. In addition, the results also show that the adsorption capacity of CO₂ first increases and then decreases with the increase of the temperature, which indicates that the optimum temperature exists for the adsorption of CO₂. This work can provide critical insights into understanding the microscopic displacement mechanism of shale oil by CO₂ in organic nanopores in shale oil reservoirs and lay a solid foundation for the CO₂ flooding in the shale oil reservoir and the CO₂ storage.