A control parameter optimizing system comprising: - an objective function setting section adapted to set an objective function to be optimized in controlling the operation of an existing power plant; - a plant model adapted to simulate the operation of the existing power plant and to calculate a process amount of the plant and a value of the objective function; and - a control parameter optimizing section adapted to optimize the values of control parameters of the existing power plant using the plant model in such a manner as to optimize the objective function; wherein the control parameter optimizing section includes: - an optimization control parameter selecting section adapted to, based on control logic information extracted from a control logic database of the existing power plant, select a control parameter from the control parameters as an optimization control parameter that is for use in optimizing the objective function; and - an optimization control parameter adjusting section adapted to adjust the value of the optimization control parameter using the plant model in such a manner as to optimize the objective function characterized in that: the control logic information is made up of control logic modules interconnected hierarchically via signal lines, and the optimization control parameter selecting section is adapted to extract, as related control parameters, control parameters related to the objective function by detecting control parameters connected to a signal corresponding to the objective function in a hierarchically retroactive manner on the low-order side of the control logic modules, and select the optimization control parameter from the related control parameters. - an objective function setting section adapted to set an objective function to be optimized in controlling the operation of an existing power plant; - a plant model adapted to simulate the operation of the existing power plant and to calculate a process amount of the plant and a value of the objective function; and - a control parameter optimizing section adapted to optimize the values of control parameters of the existing power plant using the plant model in such a manner as to optimize the objective function; - an optimization control parameter selecting section adapted to, based on control logic information extracted from a control logic database of the existing power plant, select a control parameter from the control parameters as an optimization control parameter that is for use in optimizing the objective function; and - an optimization control parameter adjusting section adapted to adjust the value of the optimization control parameter using the plant model in such a manner as to optimize the objective function characterized in that: the control logic information is made up of control logic modules interconnected hierarchically via signal lines, and the optimization control parameter selecting section is adapted to extract, as related control parameters, control parameters related to the objective function by detecting control parameters connected to a signal corresponding to the objective function in a hierarchically retroactive manner on the low-order side of the control logic modules, and select the optimization control parameter from the related control parameters. the control logic information is made up of control logic modules interconnected hierarchically via signal lines, and the optimization control parameter selecting section is adapted to extract, as related control parameters, control parameters related to the objective function by detecting control parameters connected to a signal corresponding to the objective function in a hierarchically retroactive manner on the low-order side of the control logic modules, and select the optimization control parameter from the related control parameters.