The reliability of the core control network-element S-CSCF in IMS is the key to assure the continuity of IMS services as well as the precondition to deploy the commercial IMS networks. Based on the analysis of S-CSCF’s functions and features, the paper proposes an approach to design and implement an S-CSCF reliability scheme, and discusses in detail the contents and occasion to be backed up in the process of the S-CSCF providing services, the policy to assure data consistency, fault detection, switch in the main and standby server, recovery as well. Additionally, we carry out an experiment on S-CSCF with the reliability scheme in the OpenIMSCore, an open source project. The results show that the reliability scheme is not only feasible and effective, but also costs less in data backup. When the main S-CSCF1 goes wrong, the standby S-CSCF2 can rapidly recover without influencing the experience in user’s enjoying services.