Abstract: The domestic gas storages are mainly transformed from depleted oil/gas reservoirs. However, the gas storage usually has high demands for well quality, so in principle, the gas storage should not use old wells; even if old wells are used, they must be treated properly first, and then used as gas producer or observation well on condition that their sealing performance and safety must meet the completion requirment of gas storage. Replacing the casing head is a key measure in the utilization of old wells. This paper presents the casing head structure, principles, selection and the method for replacing and installing casing head for old wells. Casing head replacement was performed on two wells and after one injection-production period, the casing was well sealed with no leaking. Through evaluating the expenses occurred, this measure saves about 50 million Yuan compared to single well year-on-year, producing remarkable economic benefits.