A flexible coal-fired power generation system includes a thermal system for coal-fired power generating unit and a high-temperature heat storage system connected in parallel, wherein: the heat storage system includes a heat storage medium pump (17), a cold heat storage medium tank (18), a hot heat storage medium tank (20), multiple valves, and a heat storage medium and feedwater heat exchanger (21). A heat storage medium heater (16) locates in the boiler (1) and is connected with both the cold heat storage medium tank (18) and the hot heat storage medium tank (20). Through the heat storage medium pump (17), the flow of heat storage medium that enters the heat storage medium heater (16) is adjusted to reduce the output of the steam turbine when the boiler (1) is stably burning.