This invention discloses a call processing method based on a BAC cluster, and a BAC clustering device. The method comprises the following steps: an entry BAC device receives a SIP (Session Initiation Protocol) message sent by a calling terminal; the entry BAC device replaces a calling terminal address in a contact header of the SIP message sent by the calling terminal with an intranet address of the entry BAC device, and transmits the intranet address to a backend BAC device; and, the backend BAC device replaces the intranet address of the entry BAC device in the contact header of the SIP message sent by the entry BAC device with an internet address of the backend BAC device, and sends the internet address to a called terminal. The method and the BAC clustering device can cluster a plurality of BAC devices, can dynamically allocate the BAC processing resource in the cluster according to the BAC load, are suitable to all the SIP users accessing the IMS (IP Multimedia Subsystem) network through the BAC, can share the load of signaling message handling, can improve the running efficiency of the network, can reduce the BAC deployment cost of an enterprise, and can improve the flexibility of deployment.