The present invention discloses a communication device applicable to a stacking communication system. The communication device comprises: a plurality of communication ports operable to constitute a part of an internal transmission path of the stacking communication system; a storage unit operable to store a reference path table; and a controller operable to receive a frame and then determine whether the frame should be forwarded, wherein if the frame should be forwarded, the controller is operable to choose one among the communication ports according to the reference path table and the content of the frame to forward the frame or a frame derived therefrom to the internal transmission path of the stacking communication system.