By regulating the doping site and concentration of Li atoms in β1-Graphyne, more charges accumulate on the surrounding C atoms and the gas-framework interaction increase, thus creating a favorable environment for CO2 adsorption and an ultra-high CO2 adsorption capacity and CO2/N2 selectivity in Li-β1-GYs. Display omitted •Li-β1-GYs exhibit an ultra-high CO2 adsorption capacity and CO2/N2 selectivity.•Li doping has a more pronounced effect on enhancing the CO2−Li-β1-GYs interaction.•Gas distribution analyses demonstrate Li doping provides more adsorption sites. The selective CO2 adsorption is of great significance to many energy and environment-related processes. Herein, CO2/N2 adsorption and separation in Li-doped 2D graphyne allotrope (β1-GY) were studied by using grand canonical Monte Carlo simulation and density(GCMC) functional theory approaches(DFT). The results showed that Li atoms were stably combined with β1-GY and the binding energy was −2.85−−3.60 eV, which ensured the structural stability of Li-doped β1-graphyne (Li-β1-GY) for CO2/N2 adsorption and separation. Different Li doping types were evaluated, and five Li-β1-GY structures were screened, including the a, b, c, ac, and bc structures. Li doping provided more adsorption sites and improved the CO2 adsorption performance. Among all Li-β1-GYs, the ac structure showed the best CO2 adsorption performance. The CO2 adsorption capacity of ac structure reached 11.10 mmol−1 g−1 at 298 K and 100 kPa, which was higher than the well-known metal–organic framework Mg-MOF-74 (∼8.60 mmol−1 g−1) under the same condition. At 298 K and 100 kPa, the CO2/N2 selectivity reached 354. The gas distribution confirmed that CO2 was adsorbed around the Li and C atoms and demonstrated the significant improvement of C atoms around Li atoms on the CO2 adsorption. The interaction analyses showed that Li doping enhanced the CO2-framework interaction more distinctively than the N2-framework interaction, leading to an ultra-high CO2 adsorption capacity and CO2/N2 selectivity. Results of this work highlighted Li-β1-GYs as promising materials for CO2/N2 adsorption and separation.