A method for implementing Wide Area Centrex (WAC) service includes that the calling party calling controller sends the Wide Area Centrex WAC group internal short number of the calling terminal to the called terminal through the called party calling controller. In which, the calling terminal initiates calling to the calling party calling controller; the calling party calling controller initiates calling to the called party calling controller, and sends the WAC group internal short number of the calling terminal to the called party calling controller; the called party calling controller initiates calling to the called terminal, and sends the WAC group internal short number of the calling terminal to the called terminal. With applying the method of present invention, it could improve the user experience of WAC service. And a system and a calling controller and an application server for realizing Wide Area Centrex service are also disclosed.