Abstract The system is based on the online communication system Ajax + Asp.net.Tt goes with Microsoft SQL Server database and VS2005.net as its development platform. It uses Ajax technology to achieve a free online communication refresh. It can meet the function of online communication as follows: The first sign of the user name and password will be saved, When the next ,the system will automatically verify the corresponding user name and password. When users have entered the online exchange system, he can see online staff. You can click on it so that you will communicate with others.The content of chatting in private can only be seen each other.In addition,users can clean screen by hands and choose font colors as well as chatting expresstions.The interface of the system for communication is simple and pretty and you can exit from the online communication system. Keywords: online communication;Register ;expression