A method and an apparatus for migrating a virtual machine across virtualization systems, and a system, where a first virtualization system in which a source virtual machine is located specifies a temporary address of a destination virtual machine. After a second migration tool of a second virtualization system migrates the to-be-migrated virtual machine to the second virtualization system to generate the destination virtual machine, a first migration tool of the first virtualization system controls a migration agent on the destination virtual machine to modify the address of the destination virtual machine to an address of the source virtual machine such that the address of the virtual machine remains unchanged before and after migration, thereby shortening service interruption duration caused by virtual machine migration.