Ansai field is a typical field with low permeability, low pressure, low production and the water flooding is inefficient. In order to explore an effective developing method for increasing the production and ultimate recovery, we carried out the feasibility studies of natural gas flooding. This paper analyses the feasibility of natural gas flooding from the geological condition of Ansai field at first, then introduces the high pressure slim tube tests for determining MMP of injection gas and reservoir oil and prediction of MMP with published correlation. The high precision correlation has been selected for predicting the composition of injection gas in miscible displacement. The performance of natural gas flooding have been simulated using MVIP simulator. The results shows that Ansai field shares the geologic conditions for natural gas flooding. The MMP of lean gas and Ansai reservoir oil is above 32MPa, and the average reservoir pressure is only 8.81 MPa in Ansai field, so the lean gas flooding is immiscible displacement at Ansai reservoir condition. If accomplishing a miscible displacement at the same condition, the composition of injected gas must be changed by increasing rich gas content, the content is 80%C2H6. The results of numerical computations shows that the recovery ratio of natural gas flooding (26.3%OOIP) is more than of water flooding (20.6%OOIP).Obviously, the natural gas flooding is a hopeful EOR method in Ansai field. These studies provides scientific evidence for the policy of natural gas flooding in Ansai field.