A realizing method of emergency registration is disclosed. When the user equipment in the visited network initiates an emergency registration request, the method comprises the following steps: after P-CSCF of the visited network receives the emergency registration request sent from the user equipment, it forwards the message to S-CSCF of the home network. The S-CSCF sets the emergency registration expiration time according to the setting policy for emergency registration expiration time, includes it into the emergency registration response sent to the P-CSCF which retrieves the emergency registration expiration time from the emergency registration response and sends the message to the user equipment, which in turn retrieves the emergency registration expiration time from the emergency registration response. The factors of the setting policy for the emergency registration expiration time comprise: a type of the emergency call, the location information of the visited network and the location information of the user equipment.