The invention belongs to the field of optimal operation of wet cooling units, and discloses an exhaust steam pressure optimizing method of a steam turbine of a wet cooling unit. The method comprises the following steps: determining heat, taken away by the cooling of circulating water, of exhaust steam of a steam turbine and the temperature of the circulating water, wherein the heat and the temperature of the circulating water are regarded as set conditions; selecting different operation modes of a circulating water pump, recording exhaust steam pressure of the steam turbine corresponding to each operation mode of the circulating water pump, and calculating difference between the power increment of the steam turbine corresponding to the unit and the power consumption increment of the circulating water pump; determining the maximum of the difference, selecting the operation mode of the circulating water pump corresponding to the maximum as an optimal operation mode in the set conditions, and selecting the exhaust steam pressure corresponding to the optimal operation mode as the best exhaust steam pressure in the set conditions; changing the heat, taken away by the cooling of the circulating water, of the exhaust steam of the steam turbine and the temperature of the circulating water to obtain optimal operation modes and best exhaust steam pressures in different set conditions. The method disclosed by the invention can direct the economical and optimal operation of the wet cooling unit more accurately.