An network system control method includes: planning an optical tunnel network according to a routing path table and transmitting a control command according to an optical tunnel network configuration of the optical tunnel network by a tunnel scheduling module, wherein the optical tunnel network includes multiple optical tunnels, and each of the optical tunnels includes a routing path and a wavelength; outputting a control signal to multiple optical switches and multiple top-of-rack switches according to the control command by a configuration managing module; receiving flow statistics of the dataflows of the optical tunnels from the top-of-rack switches, calculating dataflow rates of the dataflows and bandwidth usage rates of the optical tunnels, and transmitting a load notification when one of the bandwidth usage rates exceeds an preset interval by a bandwidth usage monitor; and replanning the optical tunnel network according to the load notification by the tunnel scheduling module.