Abstract: Water-gas alternate injection way is often adopted on well site to decrease gas fingering during CO_2 miscible displacement.In order to make a study on the influence of CO_2 miscible displacement on enhanced oil recovery in Yushulin oilfield,the long core test is carried out and the influence of total gas slug,gas slug size by water-gas in- jection way,oil saturation and water-gas ratio on en- hanced oil recovery are all studied.The results prove that all these factors are of great importance for CO_2 miscible displacement under the same condition and the optimum injected gas is 0. 3-0. 4PV.Under the condition of misci- ble phases,at least one≤0. 1PV CO_2 slug should be pre -injected or discontinuously injected in order to achieve the greatest water-gas injection effect.