A method for controlling a main feed-water pump and a main feedwater control valve including a downcomer feed-water valve and an economizer feed-water valve to control a steam generator level of a steam generator of a nuclear power plant, comprising: performing, by a proportional-integral, PI, controller, a PI operation on a compensated steam generator error signal generated according to a deviation between the steam generator level and level setpoints of the steam generator and generating a flow demand signal according to the result of the PI operation; determining, by a power determiner, whether a power section of reactor power belongs to low power section or high power section; generating, by a main feed-water controller, a main feed-water control signal for controlling the main feed-water pump and the main feedwater control valve according to the flow demand signal and the determined power section; providing, by an information provider, PI information comprising a gain and an integral time constant set according to the reactor power; characterized in that the method further comprises the steps of: determining, by the power determiner, a transfer time when the determined power section is transferred from the low power section to the high power section or vice versa; providing, by an information transformer, the PI information to the PI controller and providing transformed PI information comprising a transformed gain and a transformed integral time constant to the PI controller only for a predetermined timer time at the transfer time; wherein the transformed gain and the transformed integral time constant are preset to vary with the timer time. performing, by a proportional-integral, PI, controller, a PI operation on a compensated steam generator error signal generated according to a deviation between the steam generator level and level setpoints of the steam generator and generating a flow demand signal according to the result of the PI operation; determining, by a power determiner, whether a power section of reactor power belongs to low power section or high power section; generating, by a main feed-water controller, a main feed-water control signal for controlling the main feed-water pump and the main feedwater control valve according to the flow demand signal and the determined power section; providing, by an information provider, PI information comprising a gain and an integral time constant set according to the reactor power; characterized in that the method further comprises the steps of: determining, by the power determiner, a transfer time when the determined power section is transferred from the low power section to the high power section or vice versa; providing, by an information transformer, the PI information to the PI controller and providing transformed PI information comprising a transformed gain and a transformed integral time constant to the PI controller only for a predetermined timer time at the transfer time; wherein the transformed gain and the transformed integral time constant are preset to vary with the timer time. determining, by the power determiner, a transfer time when the determined power section is transferred from the low power section to the high power section or vice versa; providing, by an information transformer, the PI information to the PI controller and providing transformed PI information comprising a transformed gain and a transformed integral time constant to the PI controller only for a predetermined timer time at the transfer time; wherein the transformed gain and the transformed integral time constant are preset to vary with the timer time.