The present invention is a method of optimizing a process recipe of a substrate processing system including: a substrate processing apparatus that performs a film deposition process of a substrate to be processed according to a process recipe; a data processing unit that executes a calculation for optimizing the process recipe; and a host computer; the substrate processing apparatus, the data processing unit, and the host computer being connected to each other through a network. The present invention includes the steps of: measuring a film thickness of a substrate to be processed that has been subjected to a film deposition process by the substrate processing apparatus; sending a command for conducting a process-recipe optimizing process from the host computer to the substrate processing apparatus, when the measured film thickness is deviated from a target film thickness and the deviation is beyond an allowable range; and in response to the command for conducing a process-recipe optimizing process from the host computer, sending required data from the substrate processing apparatus to the data processing unit, causing the data processing unit to execute a process-recipe optimizing calculation to calculate an optimum process recipe for achievement of the target film thickness, and updating the process recipe in the substrate processing apparatus based on the calculated result.