Based on two samples of gas leakage cases of the PE electrofusion socket for gas distribution systems within 22 and 25 years of service respectively, it was analyzed that the apparent performance and structural aging performance of electrofusion socket. The results suggested that it was happened to PE electrofusion socket of aging, decrease of thermo-oxidative stability and crystallinity, thus resulting in significant deterioration of structural performance in comparison to the pipe wall. In order to clarify the structural weakness of gas leakage, the failure analysis was carried out.