WTO推行「關稅簡化（tariff simplification）」的目標是將目前仍屬於非從價關稅的商品轉為以從價關稅的方式課徵。本文建構一個三國兩廠商的垂直差異化模型，並以高、低品質廠商在從量關稅下之價格加權，計算出等量從價關稅（ad valorem equivalents, AVE）稅率，分析關稅簡化對高、低品質廠商的利潤以及社會福利的影響。本文的主要發現：關稅簡化後，外國高品質廠商的利潤會下降，低品質廠商利潤的變化則取決於兩產品的品質差距和邊際成本的大小。而關稅簡化對消費者剩餘、關稅收入及進口國社會福利的影響皆有可能提高或下降，取決於邊際成本的大小、兩產品的品質差距及AVE權重的大小。

The WTO promoted “tariff simplification” in the Doha Round, calling for the transformation of non ad valorem tariffs into their ad valorem equivalents (AVE). We construct a vertically differentiated model to examine the welfare effects of tariff simplification. We calculate the AVE based on the corrected price weighted between the prices of the high-quality good and low-quality good under a specific tariff. We find that tariff simplification will reduce the profit of the high-quality firm but its effects on the profit of the low-quality firm depends on the quality difference of the two goods and marginal cost of the firm. In addition, the tariff simplification may raise or reduce the tariff revenues, the consumer surplus, and the social welfare of the importing country depending on the magnitude of the marginal cost, the quality differences of the two goods, and the AVE weight of the high-quality good's price.