Abstract: Supercritical coolingwater reactor is a once-through cycle plant system which is different from the existing light-water reactor, so it’s important to research its perturbation. In order to maintain power plant operation stable after perturbation, we must rely on control system regulate to achieve stable state. Using FORTRAN program to make code, when perturbation happens such as pressure set-point changes, feed-water temperature drop, reactor parameters changes with time were researched at the control rod, steam turbine control valves and the reactor coolant pumps as the plant control system. The results show that feedwater flowrate perturbation will not have a significant impact on system behavior. The feedwater temperature decrease perturbation need longer time to stabilize. Pressure setpoint change has shorter time to stabilize.