The invention belongs to the field of information safety, providing a digital content safeguard system based on transparent encryption and decryption. The system comprises a transparent encryption and decryption module, an access control module, a monitoring module, a certificate authority module, a communication proxy module, a management center and a permission server module, wherein the transparent encryption and decryption module, the access control module and the monitoring module are on a client side, and the management center and the permission server module are on a server side; the client side and the server side are connected by the communication proxy module and the permission server module. Aiming at the safeguard system, the invention provides a dynamic encryption and decryption method which carries out encryption and access control to digital content as well as opens, reads and writes cipher texts. The method realizes transparent encryption and decryption to the digital content by realizing filtering driving on the bottom layer of an operating system and records an intact log to all operation of a user, thus improving system safety, and greatly improving encryption and decryption speed. Compared with the existing like products, the system of the invention has the advantages of safe and efficient encryption mode, fine grit access control, perfect log audit function and convenient and efficient management mode.