關稅隨著進口品之加工層次提昇其稅率也越高的現象，即所謂關稅調升（tariff escalation）。此一現象普遍存在於已開發以及開發中國家。在WTO 新回合談判過程中，部分國家提案要求降低原料與成品之間的進口關稅級距，本文之目的即在於探討降低關稅級距之經濟效果。本文首先建立一理論模型，由理論結果顯示，最適關稅級距決定於兩國既有之原料與成品之加工成本以及進口關稅水準之高低。當進口國既有之關稅稅率足夠高且其產業越有競爭力時，該進口國應當建議WTO 所有會員國調降關稅級距，此時將導致該國之福利水準上升的可能性越大。反之，當該國既有之關稅稅率相對較低時，則關稅級距之調整對該國福利水準之影響方向便無法確定。其次，本文應用一多國多部門之一般均衡模型，以模擬分析各國調降關稅級距對台灣經濟之影響。由模擬結果顯示，整體而言，各國調降關稅級距對台灣之社會福利有正面影響，惟對台灣大部分之農畜產品與食品加工業之生產將造成一些不利影響。 It is a prevailing phenomenon in developed countries as well as developing countries that the tariff rates of commodities are increased following their processing stages, which is known as “tariff escalation’. Some countries have proposed in the Doha round of WTO to reduce the differences in the tariff rates between intermediate products and final products. The purpose of this paper is to investigate the economic impact of reducing the degree of tariff escalation. Firstly, a theoretical model is constructed to examine the optimal degree of tariff escalation. It shows that the optimal degree of tariff escalation depends on their relative tariff levels and marginal production costs between exporting countries and importing countries. The lower the marginal production costs in the importing country, it is more likely that a decrease in the degree of tariff escalation may increase the country’s welfare if its initial tariff levels are high enough. However, the impact of the optimal degree of tariff escalation of the importing country is indeterminate if the initial tariff levels are not high enough. Secondly, a computable general equilibrium model is utilized to evaluate the effects of lowering the degree of tariff escalation on Taiwan’s economy. The results reveal that lowering the degree of tariff escalation, as proposed in the Doha Round of WTO, might enhance Taiwan’s social welfare, whereas it may cause some adverse effect on the production levels in most of Taiwan’s agriculture, poultry and processed food industries.