A hitless multi-carrier spectrum migration method executed by a network device when a consecutive idle spectrum area of an optical fiber managed by the network management system cannot meet a transmission requirement of a new service, wherein the method comprises: obtaining a spectrum of a secondary carrier and a to-be-migrated carrier in a target carrier group from a network management system, and generating the secondary carrier according to the spectrum of the secondary carrier; sending (S102, S301) a migration notification to a peer network device, wherein the migration notification comprises an adding notification and a removing notification, wherein the adding notification is carried in an optical sub-channel transport unit, OTUsub, frame borne on the secondary carrier, indicating that a carrier that bears the adding notification is the secondary carrier, and the removing notification is carried in an OTUsub frame borne on the to-be-migrated carrier, indicating that a carrier that bears the removing notification is the to-be-migrated carrier in the target carrier group, and performing answer response to a migration notification from the peer network device, wherein the answer response is used to determine that network devices at both ends can perform spectrum migration; sending (S103, S303) migration signaling to the peer network device, wherein the migration signaling is used to instruct the peer network device to migrate overhead information and a service in the OTUsub frame that is borne on the to-be-migrated carrier in the target carrier group to the OTUsub frame borne on the secondary carrier; and receiving (S104, S304) the migration signaling sent by the peer network device, and migrating, according to the migration signaling, overhead information and the service that are borne on the to-be-migrated carrier in the target carrier group to the secondary carrier, wherein after the service that is borne on the to-be-migrated carrier is migrated to the secondary carrier, a source network device and a destination network device separately send idle signaling to each other, wherein the idle signaling indicates that the service has been migrated, and an idle spectrum corresponding to the to-be-migrated carrier and its adjacent idle spectrum form a consecutive idle spectrum area, wherein a spectral width of the consecutive idle spectrum area is not less than a spectral width required to transmit the new service. obtaining a spectrum of a secondary carrier and a to-be-migrated carrier in a target carrier group from a network management system, and generating the secondary carrier according to the spectrum of the secondary carrier; sending (S102, S301) a migration notification to a peer network device, wherein the migration notification comprises an adding notification and a removing notification, wherein the adding notification is carried in an optical sub-channel transport unit, OTUsub, frame borne on the secondary carrier, indicating that a carrier that bears the adding notification is the secondary carrier, and the removing notification is carried in an OTUsub frame borne on the to-be-migrated carrier, indicating that a carrier that bears the removing notification is the to-be-migrated carrier in the target carrier group, and performing answer response to a migration notification from the peer network device, wherein the answer response is used to determine that network devices at both ends can perform spectrum migration; sending (S103, S303) migration signaling to the peer network device, wherein the migration signaling is used to instruct the peer network device to migrate overhead information and a service in the OTUsub frame that is borne on the to-be-migrated carrier in the target carrier group to the OTUsub frame borne on the secondary carrier; and receiving (S104, S304) the migration signaling sent by the peer network device, and migrating, according to the migration signaling, overhead information and the service that are borne on the to-be-migrated carrier in the target carrier group to the secondary carrier, wherein after the service that is borne on the to-be-migrated carrier is migrated to the secondary carrier, a source network device and a destination network device separately send idle signaling to each other, wherein the idle signaling indicates that the service has been migrated, and an idle spectrum corresponding to the to-be-migrated carrier and its adjacent idle spectrum form a consecutive idle spectrum area, wherein a spectral width of the consecutive idle spectrum area is not less than a spectral width required to transmit the new service.