The most important function of the Instant messaging system is immediate exchange of information, As long as the other side to remember the number, regardless of where he was, you can chat with him at any time tool exchange.This system uses C/S model constructed by the client and server components. Servers can be deployed in the same LAN, which will facilitate the conduct of safeguarding and ensuring the same enterprise information security and network resources are fully utilized. As long as the client server machines complete name or IP address, they can login and use. The current network company provide useful chat tool is that only can connect into network, So, this limit the scope of customers to some degree.This system has no restriction in this regard, as long as they are in the same LAN, they can communicate. The system use SQL Server 2000 database storing information, socket connectting the client and server , also use reported socket sending Message. Use of the system you can share some simple, do some small file transfer and information changes.