本文主要討論：若廠商之防污努力的投入具有外溢效果，則政府在訂定最適補貼率時，有無將外溢效果納入考量對補貼率訂定之影響。其次，本文亦討論當政府訂定補貼率時，外溢效果存在的考量與否，對廠商之最適產量及污染排放量之影響與傳統文獻不同。根據本文研究發現，若政府在訂定補貼率時亦將外溢效果納入考量，則可減低補貼對廠商產量之衝擊，使產量較接近最適產量。另外，加入外溢效果之考量後，補貼所達成之降低污染排放水準亦不致被高估。

According to the discovery of this article, if the spillover effect has be taken into consideration by the government when deciding the subsidy rate, it may decrease the impact on the output of the merchant, and enabling the output comparatively to approach the optimal output. Moreover, the subsidy can help to achieve in reducing the pollution discharge, which cannot be overestimated.