本文主要是探討掌握關鍵要素的既存廠商，在面對一群偏好為異質性消費者，以及提供要素給生產水平差異產品的下游競爭廠商時，是否會對下游競爭者採取市場封殺的議題。再者，為了避免產業的不公平競爭，本文更進一步從社會福利的觀點，分析政府是否應介入，將該既存廠商強制分割為上、下游獨立的兩家廠商的問題。本文主要結論是：當市場為完全覆蓋時，既存廠商會對下游競爭者採取市場封殺的策略。另外，政府是否須將該既存廠商強制分割為上、下游獨立的兩家廠商以達到社會福利最大，必須根據產品價值、生產成本與偏離消費者最偏好產品屬性之單位效用損失大小而定。

This article studies the market structure in which a monopolist upstream has control over the key factors of production but competes in Hotelling-type differentiated products downstream. A two-stage game theoretic model is set up to explain the optimal strategy for vertically-integrated leading firm. In addition, this study analyses the welfare effects of the regulator’s vertical disintegration policy and shows that the policy improves social welfare only if the niche of product differentiation has been exhausted.