The invention discloses a thermal power unit sliding pressure optimizing and regulating system and method. The system comprises a PLC control unit, a distributed control system, a plurality of steam turbine septum valves, a variable-frequency condensate pump and a deaerator level control valve, wherein the distributed control system is connected with the PLC control unit through a two-way interface, the steam turbine septum valves are connected with the distributed control system, and the PLC control unit is used for achieving system parameter and signal reading through the distributed control system and achieving control over main steam pressure, the variable-frequency condensate pump and the deaerator level control valve. By means of the thermal power unit sliding pressure optimizing and regulating system and method, time-consuming and labor-consuming unit operation optimizing experiments and calculation are avoided, a set target of the main steam pressure can be dynamically optimized in real time according to environment changes, contradiction between main steam pressure optimizing capacity and load regulating capacity is avoided through the energy storage and regulation function of a condensate system, and the maximization of operating economy of a generator unit is dynamically achieved in real time under the premise that requirements of a power grid are met.