To provide a control method of a deaerator water level control valve for reducing a reduction width of an electric power load by sending a maximum condensate quantity to a deaerator while protecting a residual pump at load run back time performed when either one of a condensate pump or a condensate booster pump trips, and a power generation plant using this method.

At load run back time performed when either one of condensate pumps 6 or 7 composed of a plurality, in the first place, a pressure drop in the deaerator 12 is restrained by squeezing the deaerator water level control valve 10. Afterwards, the deaerator water level control valve 10 is opened again while restricting opening so that the residual pump of the condensate pumps does not cause an excessive flow rate. This control method is adopted for recovering a water level in the deaerator 12.