Abstract: In a method and system of controlling the operation of a plant by means of an electronic computer, the judging conditions and control and supervisory operations corresponding thereto are described in tables from which a plurality of action lists having a standard form of plant state judging conditions plus controlling and supervisory operations are prepared. The contents of the action list are stored in the memory device of the computer. A process signal corresponding to a state of the plant is compared with a reference signal for producing a trigger signal which is used to select a corresponding action list. The content of the selected action list is judged to produce a control signal for controlling the plant.