SIP registration method for server to actively inform user switching, system and device thereof

The invention discloses a SIP registration method for a server to actively inform user switching, which is applied to a system comprising a voice terminal, a master server and a standby server. The method comprises the following steps: the standby server sends a notification message to the voice terminal according to voice terminal information which is synchronously registered from the master server after learning that the master server is not available so that the voice terminal is switched into the standby server. The invention helps avoid the problem that the user frequently sends a registration message to the server, which is superior to the existing registry backup plan.