Abstract: With the continuous improvement of EOR technology by natural gas injection process, gas injection and miscible flooding has become significant technical means to EOR. In view of the geology and exploitation of S reservoir, based on the indoor experiment and fluid phase fitting,the method of displacing near miscible phase was put forward.By using the pseudo group phase equilibrium component simulation technique, the improvement of the recovery rate of natural gas huff and puff was optimized and the recommendation scheme used in the field was designed. It provides certain technical support for the feasibility design of enhanced natural gas stimulation in S reservoir and similar light oil reservoirs.