The issue of stock valuation remains a major business concern for companies, given that the tax system formally regulates the valuation of stock by sector of activity. To get rid of this problem, it is strongly advised to make the stock zero but as we do not have this possibility, we are in the obligation to manage the stock in an optimal way from where the necessity to adopt a rational method from which we must put the accent on the economic quantity to order, the delay of replenishment and the threshold of the stock especially for the spare parts and raw material in case of a process with tended flow.