The issue of the board size includes sub-issues such as the number of directors and the structure of the board. Most management scholars believe that the number of directors, the proportion of different types of directors, and the power distribution between the board and managers, are important factors affecting the cost and performance of the board. The board size is also an interesting legal issue because it is subject to the company law. The existing Company Law of the People’s Republic of China sets upper and lower limits both on joint stock companies and limited companies. Such a strict legislative model is unique in the world. According to classical political theory, the recognition of free people is the most fundamental origin of the legitimacy of law. Therefore, the companies themselves are supposed to discover corporate governance pattern themselves. Is it necessary for legislators to set a limit on the number of directors? If so, should such limit be or permissive? What are the theoretical basis, the purpose, and the real effects of such a norm? This article attempts to answer the questions raised above.