本文以兩階段、雙占模型探討政府所面臨的關稅與環保政策組合，並推導出三種可能出現的最適政策體制。最適關稅跟環保標準有可能同時為正值，另外，也有可能出現污染補貼與關稅，或是進□補貼與環保標準的組合。嚴格環保標準出現的一個前提是要有足夠的壟斷租金。本文同時也推導出子博奕完美的成本效益政策法則並顯示有二十八種不同的政策區間，這些不同的區間主要是由公共污染、公司污染成本以及非污染成本等三個關鍵參數所共同決定。每個政策區間分別顯示出關稅成本效益大於、等於或是小於環保成本效益，也就是對政府而言，那個政策的租金移轉功能比較強。

We discuss a model where the government is faced with a choice of an optimal policy mix of environmental standards and tariffs. We show that there are three possible combinations of optimal policy portfolio, namely positive tariffs and environmental standards, pollution subsidies and tariffs, import subsidies and positive environmental standards. Regardless of the types of policy portfolio, a stricter environmental standard can be sustained by a sufficiently large monopoly rent. We derive the subgame perfect benefit and cost policy rule and show there are multiple policy regions through the interplay of abatement technology, non-abatement technology, and public abatement parameters. Each policy region suggests whether the tariff benefits/costs dominate, or are dominated, by the environmental benefits/costs, i.e. which instrument is ultimately more effective for government rent-shifting purpose.