Abstract: It analyses in detail the file system filter driver to achieve transparent encryption especifically how to deal with the transparent encryption process，including the encryption in the pre—reading process of decryption and in the writing process，and proper clearance in bufer operation．Besides，it analyses how to control the Cache Manager on the impact of encryption．It points out a number of points in the actual development process which need attention．It is useful for the development of transparent encryption software．

Key words: file system filter driver；transparent encryption；cache manager