Abstract: A plant operation support system of the present invention is characterized by the following: The present invention relates to a plant operation support system which performs process simulations in parallel with operations of an actual plant and predicts operations of the actual plant on the basis of the results simulated. The plant operation support system modifies a simulation model on the basis of actual data as required, modifies the simulation model on the basis of actual data received from the actual plant, and uses the modified simulation model to perform simulations in parallel with operations of the actual plant. Accordingly, the plant operation support system can reflect plant status in the simulation model consecutively and predict operations of the actual plant in a highly accurate manner.