本文設立一簡單貿易模型，在出口國廠商握有中間原料之假設下，探討並評估 進口國之關稅結構與進口政策。由結果得知，在追求福利極大下，進口國所訂定之最適產 品進口稅將高於最適原料進口稅，此一關稅結構現象為加工層次愈高者其關稅稅率也愈高 之調升性關稅(tariff escalation)提出理論證明。再者，本文也發現進口國究竟應採行 何種進口政策，須視其政策目標而定。當國內外生產最終產品之單位勞動成本相等時，若 進口國政府著眼於保護國內生產者，則應採取只允許原料進口之進口政策；若強調關稅之 收入，則應採取只允許產品進口之進口政策；若重視消費者或全國福利水準，則應採取同 時允許原料與產品進口之進口政策。最後，本文也證明了同時允許原料與產品進出口之貿 易型態能同時滿足進出口國福利之極大，此一結果也為世界各國同時進出口原料與產品之 貿易型態的普遍性提出理論的解釋。

　　　　　This paper develeps a simple model to investigate tariff structure and import policy. It shows that to maximize welfare the importing country has an incentive toimpose a higher tariff on the final good than on the intermediate input. Such a tariff structure has been termed "tariff escalation". Furthermore, this paper shows that the import policy chosen by the importing country depends on its policy goal. Specifically, this paper shows that an import policy allowing both intermediate inputs and final goods to be traded will maximize the welfare levels of the importing and exporting countries. This result provides a theoretical explanation for the popularity of trade patterns in which both intermediate input and final good are traded internationally.