A method for realizing an Internet protocol (IP) multimedia subsystem (IMS) disaster tolerance includes the steps as follows. An S-CSCF receives a user registration, and backs up necessary data which is required when a user service processing is restored on a storage entity in a network. An I-CSCF of user's home domain receives a service request of the user, and if it is found that the S-CSCF currently providing a service for the user fails, assigns a new S-CSCF to the user, and forwards the service request to the newly assigned S-CSCF. The newly assigned S-CSCF interrogates and acquires subscription data of the user and the necessary data backed up by the original S-CSCF from the storage entity, and then restores the user service processing according to the subscription data and the backup data. A device for realizing an IMS disaster tolerance is also provided.