Abstract: Investigate the equipment and operation of 14 different capacity and type coal-fired units which operated frequently in start-stop and deep peak shaving conditions.The influences on the safety of boiler,turbine,electrical equipment and environmental protection facilities were revealed.The main influences that have appeared in frequent peak shaving units include boiler heating surface leakage,boiler oxide coating increase,serious ABS block,turbine vibration,and large temperature difference between the upper and lower cylinder.As the supercritical units have complicated thermal cycle systems and huge equipment,they have more serious safety problems when take part in start-stop and deep peak shaving.With the increasing of peak shaving operation,more potential risks such as department damage,operation risk,combustion deterioration,etc will revealed.