For most of the anticlinal, fault nose, salt dome and buried hill reservoirs in China, attic oil is easy to form during the waterflooding exploiting process, which reduces the oil recovery efficiency. The top gas injection gravity immiscible displacement process can push oil⁃water interface to the bottom of production wells and improve the final recovery efficiency. An experimental study on the gravity immiscible displacement process of top gas injection is carried out. The horizontal gas injection and top gas injection displacement processes are compared. The results show that the recovery efficiency of the top gas injection is higher than that of horizontal gas injection. Besides, four groups of the gravity immiscible displacement processes of top gas injections are compared. The results show that the final recovery efficiency can increase to a certain extent with the decreasing of gas injection rate, but the duration of the whole displacement process increases sharply. The research indicates that gravity differentiation can increase the final recovery efficiency. At the same time, in consideration of the cost of time, there is a limited gas injection rate, for which the calibration value is 2 mL/h.