Water-Alternating-Gas technology is widely used in oilfield development because it can delay gas channeling time and improve oil displacement efficiency. The gas cap reservoir naturally has the favorable material basis for the implementation of Water-Alternating-Gas. Whether the gas cap energy can be used to realize the Water-Alternating-Gas in the process of gas cap reservoir development, so as to improve the oil ring recovery rate is worthy of further study. Combined with the mechanism of Water-Alternating-Gas and barrier water injection, the numerical simulation method is used to analyze the mechanism of oil-ring Water-Alternating-Gas by using gas cap energy instead of water and gas alternating injection in barrier water injection wells during the exploitation of gas cap reservoirs. The results show that the development of periodic water injection in barrier water injection wells can effectively improve the recovery degree of oil ring. At the same time, under the premise of forming water barrier, barrier water injection wells only carry out periodic water injection in gas cap or periodically reduce water injection, which can also achieve the effect of improving the recovery degree of oil ring. It is proved that the driving effect of gas cap energy on oil ring can be controlled by barrier periodic water injection, which can achieve the effect of alternating gas drive and water drive, so as to improve the development effect of oil wells. This technology has been implemented in the test well group of B reservoir, and the maximum water cut decrease of the test well group is 5%, and the maximum daily oil increase is 5 t/d. The combination of barrier periodic water injection and gas cap drive can maximize the use of gas cap energy and achieve the purpose of Water-Alternating-Gas to drive remaining oil in gas cap reservoirs economically and efficiently.