Embodiments of the present disclosure provide a backing up method, device, and system for a virtual machine. The backing up method for a virtual machine includes a backup server mounting a snapshot initial volume of a to-be-backed-up original volume of a virtual machine in a primary storage device to the backup server, creating an initialization backup volume on a backup storage device and mounting the initialization backup volume to the backup server, and backing up an original data block of the original volume to the initialization backup volume.