The bandwidth allocation apparatus includes a high bandwidth arbitration module, a low bandwidth arbitration module and a multiplexer. The high bandwidth arbitration module is used to select one downstream device from the high bandwidth downstream device group for allowing uplink. The low bandwidth arbitration module is used to select one downstream device from the low bandwidth downstream device group for allowing uplink. The multiplexer selects the one of the access requests from the high bandwidth arbitration module or the low bandwidth arbitration module for allowing to uplink the access request to an upstream device. The access transmission times of the high bandwidth arbitration module and the low bandwidth arbitration module are counted respectively by a counting circuit.