The present disclosure discloses a file access method of a virtualization instance, including performing union on some image subfiles in a host operating system (host OS) and mounting a united directory to a union directory, and when an application in a library operating system instance needs to access a file in the union directory, causing a central processing unit to generate an exit event such that a hypervisor captures and processes the exit event, and during processing, converts an access request that is from the instance into an access request based on a system call of the host OS, and performs access.