Abstract: Water alternating gas flooding(WAG) is the effective way to increase the swept volume after waterflooding and weaken the fingering phenomenon generated by the viscosity difference. QK17-2 is a waterflooding oil field. It's total water cut was more than 80 percent, which enters high water content period of mid-late development. QK17-2 oilfield faces the problems of high water content and low oil yield after waterflooding. In order to solve these problems, laboratory experiments have been carried out, including the phase state of formation fluid, nitrogen injection expansion, slim tube and long core displacement experiment. Through the results of experiments, the feasibility of EOR by N2WAG after waterflooding was analyzed. It turned out that the effect of N₂-WAG is the best, followed by waterflooding while the effect of nitrogen injection is the worst. The recovery of N₂-WAG without dip angle and with dip angle is increased by 4.46%~6.24% and 11%~12.58% respectively than waterflooding. It is concluded that the recovery of N₂-WAG with dip angle is the highest.