本文探討存在中間財市場下，貿易自由化對最適環境政策、國內污染量及福利的影響。在進口模型中，當本國之環境稅率為內生下，存在中間財市場將擴大貿易自由化降低最適環境稅率的幅度；此外，貿易自由化將提高本國之污染量，可能降低本國福利。再者不論中間財市場為獨占或完全競爭，當政府課徵最適環境稅率，貿易自由化對本國污染量與本國福利的影響皆相同。相較於進口模型，在產業內貿易模型下，貿易自由化可能提高最適環境稅率。儘管貿易自由可能提高污染稅，本國環境傷害必定提高。

This paper studies the effects of trade liberalization on the optimal environmental policy, domestic pollution, and welfare in the presence of an intermediate good market. In the import model, there is a monopoly in the domestic intermediate good market. One domestic downstream firm generates pollution during production and competes against one foreign firm in the domestic downstream market. When the domestic environmental tax is endogenous, the presence of the intermediate good market increases the reduction of the optimal environmental tax caused by trade liberalization. Moreover, trade liberalization increases the domestic pollution and may lower domestic welfare. No matter whether the intermediate good market is monopolistic or perfectly competitive, under the optimal environmental tax the effects of trade liberalization on domestic pollution and welfare stay the same. Compared to the import case, under the intra-industry trade (IIT) model the optimal environmental tax may increase after trade liberalization. Although trade liberalization may increase the pollution tax rate, it always increases the environmental damage.