The present invention discloses a route service device and a method and a system for realizing call route by the device, in which, route service device and soft switch control device are networked in a layered way, the soft switch control device is the node of the lowest layer, when the user route changes, the soft switch control device reports route information including user node to the father node; the route service device performs registration, and broadcasts the changed route information to the father node, each related route service device performs registration and broadcast by the same way; when calling across domains, the soft switch control device where the calling locates initiates inquiry toward the father node, and receives the returned inquiring result, therefore routing the call to the soft switch control device where the called locates. The present invention employs route service device to replace soft switch control device for performing call route function, therefore enabling the soft switch control device absorbed in providing services, and also providing a scheme of large scale networking at telecommunication level for soft switch control device.