The present invention discloses a network traffic control system capable of properly using bandwidth of a local area network (LAN). An embodiment of the system includes a master device and at least one slave device(s). The master device and the slave device(s) belong to the same LAN. The master device is configured to receive at least one flow notification packet(s) from each slave device, and determine flow allocation of the master device and each slave device according to the flow notification packet(s) and a total flow threshold. The master device is further configured to generate at least one flow control packet(s) according to the flow allocation of all the slave device(s) and transmit one or more packet(s) in accordance with the flow control packet(s) to each of the slave device(s), so that each slave device determines flow allocation of its executing network-dependent program(s) according to the one or more packet(s).