The invention discloses a deep peak shaving system of a thermal power plant. The deep peak shaving system comprises a superheater, a reheater, a high-pressure cylinder, a reheating steam electric regulating valve, a main steam electric regulating valve, a medium-pressure cylinder, a low-pressure cylinder, a condenser, a condensation water pump, a low-pressure heating water feeding heat exchanger,a water feeding pump set, a deaerator, a high-pressure heating water feeding heat exchanger, a steam turbine low-pressure steam extraction system, four-stage extraction, a steam turbine high-pressuresteam extraction system, a high-temperature molten salt water feeding heat exchanger, a high-temperature molten salt pump, a high-temperature molten salt storage tank, a low-temperature molten salt storage tank, a low-temperature molten salt pump, a molten salt preheater, a steam condensation type heat exchanger, a steam non-condensation type heat exchanger, a steam pressure reduction device and the like. According to the system, the molten salt heat storage technology is utilized, redundant steam heat is stored during load reducing peak shaving of a unit, in the process of load increasing peak shaving of the unit, high-temperature molten salt is used for heating high-pressure fed water to reduce steam extraction of a steam turbine, the output of the steam turbine is increased, the heat efficiency of the unit is improved, and the flexible and deep peak shaving of the thermal power plant is realized.