The invention relates to a distributed control passive optical network system and a bandwidth control method, and the system comprises a plurality of client sides, a local side and a beam split and combination device. Each client side is provided with a first sending/receiving device for transmitting and receiving data packets of a data uplink channel and a data downlink channel respectively, and a second sending/receiving device for transmitting and receiving control signals of a control channel. Uploaded data of each client side is loaded by the data uplink channel and transmitted to the local side by the beam split and combination, and the downloaded data of the local side is loaded by the downlink channel and is transmitted to corresponding client side by the beam split and combination. Network state information required between the client sides can be provided by the control signals loaded by the control channel.