To provide a plant design supporting system and method capable of easily operating the optimal design of a new plant.

An operation data collecting device 1 collects operation data from each in-service line constituting element in the plant of a factory, and an operation data base device 2 stores the collected information as a file. A data analyzing device 3 analyzes the operation data, and an operation characteristic data base device 4 stores the analyzed characteristics as a file. A production simulation device 5 constructs the model of the production system of a new plant, and sets an initial condition, and obtains and sets the operation characteristics from the operation characteristic data base device 4, and operates simulation, and feedbacks the result to the design of the production system of the new plant.