It is usually ignored in the traditional EOQ model that the opportunity cost results from lost sales when the enterprise has no commodity in the wearhouse. This paper focuses on some operating enterprise.Under the condition of time_limited partial back_orders and non_instant supply,an EOQ model is established of which it is more reasonable to assume the loss of without commodity in the warehouse divided into two parts:the opportunity cost due to lost sales and the shortage cost.It is discussed that the general cost function and the optimal solution to minimizing the total cost.The new basis of the decision of store system management is provided.Moreover,the model is applied to the example.