Abstract: The present disclosure a bandwidth allocation method including steps of: (a) providing a base station and a user equipment, wherein the base station provides a plurality of bandwidth parts for the user equipment within a service area; (b) selecting a bandwidth part from the plurality of bandwidth parts as a reference bandwidth part and utilizing the base station to transmit a reference signal through the reference bandwidth part; (c) utilizing the user equipment to receive the reference bandwidth part and output a channel report according to a channel status of the reference bandwidth part, wherein the channel report includes a channel quality indication; (d) determining whether the channel quality indication is greater than a first critical value, performing a step (e) when the determination result is not satisfied; and (e) instructing the user equipment to switch to a bandwidth part with a smaller frequency band as the reference bandwidth part.