Embodiments of the disclosure provide a method for keeping a session table alive in a Network Address Translation, NAT, apparatus, including: creating a hello session table by an Access Border Gateway Function, A_BGF, apparatus; creating a hello message by the A_BGF apparatus according to the hello session table; sending the hello message by the A_BGF apparatus to the NAT apparatus; receiving the hello message by the NAT apparatus; and updating a session table corresponding to the hello message by the NAT apparatus. Embodiments of the disclosure also provide a system and apparatus for keeping a session table alive in an NAT apparatus. Application of the embodiments of the disclosure keeps the session table alive in the NAT apparatus of an IP Multimedia Subsystem, IMS, ensures an unblocked registration path, and prevents the user conversation being interrupted due to an aged session table of the NAT apparatus.