Impurities contained in the injected CO2 will exert influence on minimum miscibility pressure (MMP) as well as the crude oil property. It is meaningful to study the influence of impurities on CO2 flooding. Based on PVT data regression, the impact of CH4 and N2 on MMP was analyzed with numerical simulation method. Besides, the impact of impurities on crude oil properties was also studied. It shows that the presence of N2 and CH4 tends to increase MMP, and the influence of N2 is more notable. When the mole fraction of injected pure CO2 reaches 60%, the oil viscosity reduces by 71.9% and the coefficient of cubic expansion reaches 1.42. But when 30% mole fraction of CH4 is contained in the injected CO2, the oil viscosity reduces by 69.72% and the coefficient of cubic expansion reaches 1.41. However, when 30% mole fraction of N2 is contained in the injected gas, the oil viscosity only reduces by 65.92% and the coefficient of cubic expansion is 1.36. For the target block, the critical molar content of CH4 in the injected CO2 is 5.6%, while the critical molar content of N2 is 2%.