本文從異質廠商的觀點切入，說明不同風險結構的廠商與共融資管道－商業銀行、投資銀行、或綜合銀行－的關係；藉此探討綜合銀行進入廠商資金市場對銀行業結構所造成的影響。由於廠商在企業經營過程中，除了面臨影響公司整體營運的事業風險外，尚順承擔專屬於投資計畫的專案風險。因此我們從廠商所面臨的風險差異，來區分不同的廠商。根據本文的結果指出，當廠商得知自己的專案風險，但無從獲悉事業風險類型時，經濟體系中低事業風險的廠商愈多，愈有利於投資銀行的經營；反之商業銀行的經營愈有利。隨著低事業風險與高事業風險廠商數量差距縮小，經濟環境愈有利於綜合銀行的經營。當廠商無從判知自己事業風險及專案風險時，高成功機率（即低專案風險）廠商數目愈多，對投資銀行的經營愈有利；反之則有利於商業銀行的經營。然而隨著高成功機率與低成功機率（即高專案風險）廠商數量差距縮小，愈有利於綜合銀行的經營。
This paper exams how the heterogeneity of firms in economic system influences the determination of banking structure. We discriminate different firms by the difference of the risks they face. In the process of enterprise running, besides the enterprise-wide risk which will result in expect-yield fluctuating, firms face the project-specific risk which belongs to specific investment project. In this paper, we suppose that when firms know their project-specific risk but not enterprise-wide risk, the bigger the quantity of the low enterprise-wide risk firms in economic system becomes, the more advantage the investment bands will take in enterprise running; Otherwise, the more advantage the commercial banks will take. The smaller the difference of the quantity between low and high enterprise-wide risk firms, the more advantage the universal banks will take in this kind of economic environment. When firms have no way to know their enterprise risk and project-specific risk, the bigger the quantity of the high success probability (love project-specific risk) firms becomes, the more advantage the investment banks will take; Otherwise, the more advantage the commercial bands will take. The smaller the difference of quantity between high success probability and low success probability (high project-specific risk) firms, the more advantage the universal banks will take in enterprise running.
