存貨管理的主要決策乃是何時訂購與訂購數量，因而在以前置時間及訂購量為決策變數的存貨模式中，再訂購點（r）為模型數理推導之關鍵，然不論Ben-Daya或Ouyang等學者，其列式或假設之再訂購點均為r=�尳+K�窬1/2，唯其依據來源及其合理性，在文中並未見有明確之推論；本文首先探究此問題之根源，其次另以單位時間需求發生之次數服從卜瓦松Poisson（λ）分配為假設，導出再訂購點之數學式，並以需求量同為常態分配之文獻範例進行數值模擬與敏感性分析，進而比較本研究的推論與原模式之差異，及驗證本模式之穩健性。 研究結果顯示：就理論上而言，原模式可視為本模式在前置時間L下，需求次數恰發生L次之特例；由模擬驗證的結果，除了確認本模式的穩健性外，亦可發現原模式之理論值與模擬值差異甚大，其原因為忽略了每次需求發生時需求量之期望值（EAC）對總需求量變異數之影響。而其在實務上之意涵為依原模式之存貨政策容易造成缺貨機率的增加。

　　　　　Traditionally, the “lead time” of inventory model is often regarded as given or random variable. In other words, the lead time is not controllable. A different viewpoint is proposed in comparison with the unit time demand hypothesis of the lead time and ordering quantities based inventory model that r(re-order point)=mL+KsL1/2 is proposed by Ben-Daya and Raouf and Ouyang. In this paper we suggests to utilize negative exponential function for crash cost, and then to construct an inventory model based on ordering quantities and lead time under the hypothesis of demand frequency and quantities corresponding Poisson and Normal distribution respectively. The result indicates: Under the reordering point specified in this paper and the same demand expectation value, the probability of the occurrence of stock insufficiency is lower than that assumed by above scholars. After simulating the actual ordering case, the variance of total expectation cost (EAC) is small relatively. This finding validates the correctness of the model and shows that the theoretical value can be utilized for practical purposes.