In cloud computing, the live migration of virtual machines (VMs) can ensure the running of cloud services. In order to enhance the performance of the whole-system migration, this paper presents a new disk migration method combined the redirect-on-write (ROW) mechanism with pre-migration and hierarchical migration to complete the live migration of VMs. At the pre-migration stage, isolates the original data and update data, simultaneously partitioned target disk for redirecting into low-frequency and high-frequency blocks according write frequency. After pre-migration stage, migrates the low-frequency blocks in the next round, then, migrates the high-frequency blocks at the shutdown stage. In this way, the amount of synchronization redundant data can be reduced. Experiments show that the technology proposed in this paper can reduce the amount of new-data migrated more than 65 percent and cut down the average migration time for 24s. It performs better in the whole-system migration, especially in the case of low workload.