Abstract: A policy group based file protection method is provided and includes the following steps. A file management driver is executed on the client device of the client. The identity data associated with a client is transmitted to the server when connection between the client and the server is established. The server determines whether the client belongs to a policy group according to the identity data. When the server determines that the client belongs to a policy group, the server transmits a certificate of the policy group to the client device. When the file management driver detects a request for executing a file open procedure, the file management driver determines whether to allow a file access application executing the file open procedure and opening the file based on the certificate received, wherein the request is executed by the file access application installed in the client device.