Most researches on VMI (Vendor Managed Inventory) evaluated its effect only from the buyer's standpoint. In fact, not only the influence on the buyer but on the whole supply chain should be considered. Based on foregoing researches, this paper tries to perfect the traditional model of VMI by taking the correlation between transport costs and economic order quantity into account. The certain cost condition in which supplier's short-term cost tends to increase is found based on the new model studying. As a middle working platform, the introduction of third-party logistics (TPL) is found to be propitious to reduce supplier's logistics costs and increase his shortterm profit under VMI, which can inspirit suppliers to take part in VMI.