The invention provides a method and system for determining an optimal flow value of a condenser circulating water pump. The method comprises the following steps: according to the specific heat capacity of circulating water, an initial circulating water flow value, a changed circulating water flow value, and an initial circulating water temperature difference, generating a changed circulating watertemperature difference by using a condenser heat balance model; according to the circulating water inlet temperature, a heat transfer end difference of a condenser and changed circulating water temperature difference, generating the steam turbine unit exhaust temperature; generating a first coal consumption influence curve according to the steam turbine unit exhaust temperature and IAPWS-IF97; according to the initial circulating water flow value and the changed circulating water flow value, generating an initial power consumption rate and a changed power consumption rate; generating a secondcoal consumption influence curve according to the initial power consumption rate and the changed power consumption rate; and generating a circulating water optimal flow value according to the first coal consumption influence curve and the second coal consumption influence curve. The method for determining the optimal flow value of the condenser circulating water pump provided by the invention hasthe beneficial effect of determining the optimal circulating water flow value under different inlet water temperature conditions and saving the operation cost of the unit.