This paper begins with an introduction of the position and function of investment banks in the macro-economy, then gives an analysis of the general connotation of investment banks and analyzes the particular implications of investment banks from the perspective of the professional service firms. On the basis, the paper analyzes the economic nature of investment banks, discusses the internal governance environment, profit distribution and recommends the two operation systems for internal governing mechanism by adopting relevant corporate governance theory and enterprises theory. Based on above description, an in-depth analysis is then further conducted to identify the various factors affecting the transition of investment banks from the partnership system to the corporation system and weigh the advantages against the disadvantages involved. Finally, the paper ends with a brief conclusion and gives suggestions on the development of investment banks in our country.