The previous methods for CO2 separation from CO2 rich natural gas led to expensive production costs. This work was implemented to overcome the problems utilizing a new approach economically. The cooling and rapid expansion processes were integrated for the CO2 separation from CO2 rich natural gas on the supercritical condition. The experimental apparatus was newly constructed to perform the experiments, and the results were simulated using a various equation of state. The result reveals that the inlet temperature of supercritical expansion diminished the outlet temperature and the gas condensed easily. The simulation indicated that the 70% CO2 in natural gas was condensed easier than 45% CO2. We found that the outlet temperature of −42 °C and the vapor fraction of 0.69 was attained at the CO2 composition of 70%. Besides, the pressure drop change influences the vapor fraction at various CO2 compositions. The vapor fraction under supercritical diminished significantly compared with the non-supercritical condition. The expansion coefficient determined utilizing the equation of state escalates by the enhancement of expansion inlet temperature based on CO2 composition in natural gas. The acid gas equation of state was the perfect equation to estimate the expansion coefficient with the absolute average error of 4.83%. This work suggests that the CO2 separation from CO2 rich natural gas with the cooling and rapid expansion method promotes the new approach to overcome the disadvantages of previous methods.