本文以Xing (2006)的三階段賽局及Grossman and Helpman (1994)的利益團體模型為基礎，並採用Fredriksson (1999)的福利函數設定，探討當市場結構為雙占，兩國廠商的商品於本國進行數量競爭時，在兩個遊說立場相左的利益團體影響下，關稅政策與環境政策的關聯。
我們發現政策主要受到外部性效果與利潤移轉效果的影響。當環保團體的力量佔上風，使外部性效果較大時，本國政府會訂定高於最適的汙染排放費；當產業利益團體的力量較強，本國政府則會訂定低於最適的汙染排放費。而不受利益團體影響的外國政府所訂定的汙染排放費則必然小於最適。
考慮關稅政策後，本文發現若外部性效果大於利潤移轉效果，本國政府可能實施補貼進口財貨的政策，並調降原先高於最適的汙染排放費。如果利潤移轉效果較大，則本國政府則會對進口財貨課徵關稅，且汙染排放費較未考慮關稅時更高。至於汙染排放費與皮古稅的相對的大小，則視政府在乎環保團體的程度而定。另外，外國的汙染排放費原則上皆低於最適。

This thesis demonstrates a situation in which two interest groups provide political contributions to influence trade policy and environmental policy in their favor. The basic model is based on Xing (2006) and Grossman and Helpman (1994). To investigate how the tariff affects environmental policy in the presence of lobbying, I establish an international duopoly model containing three stages, in which firms competing in terms of quantity in the domestic market. Pollution arises in the process of production and does not travel across the border.
I show that the equilibrium policies of the domestic country depend on the externality effect and the rent-shifting effect. I also find that under certain conditions, the externality effect can outweigh the profit-shifting effect. In this case, the domestic country’s emission fee will exceed the Pigouvian tax. Then by endogenizing the tariff, this thesis finds that a negative tariff will be given to the imported goods and the emission fee will decline. However, the emission fee will be set below the Pigouvian tax, if the rent-shifting effect is dominant. Under such circumstances, the domestic country will charge a positive tariff, and set a higher emission fee. As to the foreign environmental policy, which is not subject to the plague of the interest groups, the emission fee will be likely set below the Pigouvian tax.

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