CO2 capture and sequestration (CCS) is recognized as one of the most promising alternatives to weaken the greenhouse effect, and nanoporous materials are regarded as the promising candidates; therefore, developing a new cost-effective sorbent to achieve CCS is crucial. In this study, asphaltene-based slit nanopores were used to simulate capturing of CO2 from flue gas. The grand canonical Monte Carlo and molecular dynamics simulation methods were employed to examine the microscopic behaviors of CO2 and N-2 in asphaltene slit nanopores. The isosteric heat of CO2 and N-2 molecules adsorbed in asphaltene slit nanopores, the adsorption energy of a single molecule of CO2 and N-2 adsorbed on the surface of asphaltene fragments, and the self-diffusion of CO2 and N-2 molecules adsorbed in asphaltene slit nanopores were examined. Strong competitive adsorption of CO2 over N-2 is found in a broad range of temperatures and pressures, and it was found that the temperature plays an important role on the competitive adsorption. This work demonstrates how the competitive adsorption of CO2 over N-2 happened in asphaltene slit nanopores, which not only enriches the theoretical knowledge about gas behavior in asphaltenes but also gives the feasibility that the asphaltenes or asphaltene-based materials might be an interesting candidate for capturing CO2 from flue gas.