Mobile node (MN) is reachable based on home agent (HA) in mobile IPv6 (MIPv6). This paper proposes the active detection and transfer HA fault-tolerant method (ADTM) for MIPv6 networks. It defines the conception of ring detection & backup chain (D&B chain) among HAs in the same link. An MN only backups its registration information on the next HA in the D&B chain. For any HA, its previous HA and its next HA in the D&B chain detect the HA's validation based on neighbor discovery mechanism. If an HA is detected failure, its next HA will take over the failed HA temporarily, then inform the failure information to MNs served by the failed HA. An MN received the failure information will select a new valid and perform home registration again. For implementing ADTM, this paper defines the data structures, designs the fault-tolerant algorithm and describes the procedure in detail. It is proved that this method has less fault-tolerant time and less signal cost than the method in RFC 3775, especially in the scenario of MN moving more frequently.