本論文建立一個上下游垂直市場的理論模型，討論當上游為獨占廠商、下游為兩家之寡占廠商之下，假設下游兩家廠商之產品為異質且生產效率亦不同，探討在不同的市場規模下是否會存在垂直整合。 在本文建立的模型下發現，(1)若市場規模太小，上游廠商會合併所有廠商。(2)若市場規模小，但不會使下游所有廠商退出市場，上游廠商不會與下游廠商合併。(3)若市場有一定規模，如果下游廠商間的效率差越多，產品替代性越小，則上游廠商越有可能與高效率廠商合併；(4)如果下游廠商間的效率越接近，產品替代性越大，則上游廠商不會與下游廠商合併。若市場規模很大，上游廠商不會與下游廠商合併。 由這些發現本文有幾個結論：(1) 若兩家下游廠商之效率不接近，且兩產品替代程度越低，則當市場規模極小以及產業興起時，越可能存在垂直整合。(2)若兩家下游廠商之效率接近，或若兩家下游廠商之效率不接近，但兩產品替代程度高，則市場規模越大，越不存在垂直整合。;This paper builds a theoretical model of vertical markets with one upstream and two downstream. Then, discuss whether there will exist vertical integration in different market size with goods of downstream are heterogeneous and production efficiency of downstream are different. In this paper’s model, we can find some conclusions.(1) If market is too small, the upstream will merge all firms of downstream. (2)If market is small but there are at least one firm of downstream in the market, the upstream will not merge any firm of downstream. (3)If market is normal, the upstream may merges firm with high efficiency of downstream when efficiency of downstream lot worse and product substitution of downstream close. Or, the upstream will not merge any firm of downstream. (4)If market is too large, the upstream will not merge any firm of downstream. And we have some conclusions by these findings:(1)If efficiency of downstream lot worse and product substitution of downstream is small, then, there are the presence of vertical integration when the market is too small and the more likely the presence of vertical integration when the industrial rising(market is notmal). (2)If efficiency of downstream lot worse and product substitution of downstream close, or if efficiency of downstream close, then, there are the more unlikely the presence of vertical integration when the market increase.
