A method and apparatus for starting a virtual machine. A specific implementation of the method comprises: acquiring, by a physical machine, a mirror image file required for starting a to-be-started target virtual machine from a distributed block storage system, in response to an entered instruction to start the target virtual machine; and starting the target virtual machine by using the mirror image file. The mirror image file required for starting the virtual machine is stored in the cloud-based distributed block storage system, and a virtual disk is mapped to the physical machine. When the physical machine needs to start the virtual machine, the mirror image file required for starting the virtual machine is acquired from the cloud-based distributed block storage system by reading the virtual disk.