Although various media reported that the investment banking business model had collapsed after the so-called Lehman Shock, it is unclear what the investment banking business model is and what part of the model was the cause of the collapse. This paper aims to analyze the difference of the traditional and modern investment banking business models mainly from the relationship management perspective. From the discussion of some key factors of the business model such as tacit knowledge and organizational structure, we can conclude that the modern investment banking business model has lost its strength due to relying too much on the financial capital.