Netchina Network Security Audit System (NSA) which independently researched and developed by Shanxi Netchina Information Industry Co., Ltd is a current online production based on the content. It could upload data flow including e-mail, BBS, P2P Software, upload and download file, data base, remote login. NSA collects, analyzes, restores, audits and backups several of those messages. It effectively prevents the reveal of internal online sensitive information and transformation of illegal information through current dynamically survey network flow, network behavior and communication content.