The present invention is related to a beam division multiple access system and a method thereof. The base station according to the present invention comprises a initial mobile station information receiver for receiving initial mobile station information that a mobile station omnidirectionally transmits in an initial communication step, a mobile station location and speed detector for detecting a location and a moving speed of the mobile station from the initial mobile station information, a downlink beam generator for generating a downlink beam based on the location and the moving speed of the mobile station transferred from the mobile station location and speed detector, and adjusting at least one of a width and a direction of each the downlink beam, and a downlink beam transmitter for transmitting the downlink beam generated by the downlink beam generator to the mobile station through a phase array antenna.