Abstract: Supercritical cooling fast reactor is the once-through cooling system,and its transient safety characteristics is different from that of the existing LWRs.Under the failure transient accident of the feedwater control system,the reactor pressure,power,coolant temperature,coolant mass flow and the surface clad temperature changing with the time are studied with three different control modes（the control rods,steam turbine valves,and reactor coolant pump）.The results show that with the combined control by the turbine valve and control rod,all reactor parameters are stable and the clad temperature is within the safety range,thus the transient accident of feedwater control failure can be mitigated to ensure the safety of the supercritical fast reactors.