In this paper, a production process system simulation of the automobile relay switch manufacturing factory is studied. The status of the present production system is inspected first, and the modified model is simulated next. To inspect the effect of the process parameter change, a simulation program is developed using PROMODEL simulation software plus the EXCEL VBA and Active X Automation function. Using the developed simulation program, user can find the best production condition and alternatives on the production capacity, number of workers, and inspection status considering the defective ratio of the product. The feasibility of the new alternatives is compared with the present system using statistical method.