The invention provides an automatic virtual machine migration method and device. The method comprises the steps that for at least one monitored host, a migration threshold value corresponding to each monitored host is acquired; a target virtual machine and a target host which correspond to each monitored host are acquired; hardware resources of each monitored host are monitored to acquire a corresponding first hardware resource occupation value; whether the first hardware resource occupation value of each monitored host is larger than the migration threshold value corresponding to the same monitored host or not is judged; if yes, the migration instruction of migrating the target virtual machines running in the monitored hosts to the corresponding target hosts is formed, and then the target virtual machines are migrated. The device comprises an acquiring unit, a monitoring unit, a judging unit and an executing unit. According to the scheme, the cost of maintaining a virtual machine system can be reduced.