Abstract: To determine the minimum stock is to satisfy the effects of some factors for oil depot. For example, no oil in or out for several days. This paper inquires into the design method and establishes the stock model of oil depot system by using the theory of System Engineering as well as advances a method to determine the best stock of oil depot by using the digital simulation technique. Compared with the traditional turnover coefficient method, the system design method will be more e-conomical and reasonable than the traditional method because the interactive effect between oil depot and environment has been considered in the system design method.