中文摘要：

本文构建了一个小股东、控制股东和经理人之间的双层委托代理理论分析框架来分析我国上市公司中同时存在的两类代理问题：股东与经理人的利益冲突以及控制股东与小股东的利益冲突。在此基础上着重研究了控制股东掏空行为与公司股权结构及公司价值之间的关系。通过分析指出：（1）均衡状态下，公司的所有权集中程度由公司股东所受投资者法律保护程度决定。随着投资者法律保护程度的增加，小股东最优的投资数量也会增加，公司的所有权结构趋于更加分散。（2）在公司的现金流所有权结构确定的情况下，由股东和经理人之间的信息非对称性引起的股东和经理人之间的利益冲突会减少公司价值，使得控制股东和小股东的利益均受到损害。控制股东掏空资产收益的比例随着其自身现金流所有权的增加而减少，随着其控制权和所有权之间的分离程度而增加，随着投资者法律保护的增加而减少。（3）相对于公司中仅仅存在股东和经理人之间的利益冲突的情形，控制股东的掏空行为会进二步降低公司的价值，而且降低的程度会随着控制股东的控制权和所有权的分离程度的增加而增加。（4）当控制股东完全不能进行掏空时，即使小股东仍然面临由于公司中的第1类代理问题引起的利益损害，但均衡时，由于控制股东和小股东之间不存在利益冲突，小股东仍然会将自己全部的财富委托给控制股东，此时公司的股权结构是极其分散的。这些结论得到许多实证研究结果的支持。

英文摘要：

In this paper, we develop a base twin-principal-agency model between a minority shareholder, a controlling shareholder and a manager to analyze the two types of agency problems existing in many China＇s listed companies： the conflicts of interest between shareholders and managers as well as the conflicts of interest between the controlling shareholder and the minority shareholders. Based on this model, we mainly analyze the relationship between the controlling shareholder＇s tunneling and the concentration of corporate ownership structure as well as the firm valuation. We find that.. 1） in equilibrium, the investors＇ legal protection determines the concentration of corporate ownership structure. As the legal protection degree increases, the minority shareholders would increase the optimal investment level and the corporate ownership structure would become more dispersed. 2） After the determination of the corporate cash-flow ownership structure, the conflicts of interest between shareholders and managers would reduce the firm valuation and damage the interests of both the controlling shareholder and the minority shareholders. Tunneling hy the controlling shareholder decreases with his cash-flow rights, increases with the separation of his control rights and cash-flow rights and decreases with the investors＇ legal protection level. 3） By comparison with the case in which only exist the conflicts of interest between shareholders and managers, tunneling by the controlling shareholder would further reduce the firm value, and the degree of reduction would increase with the separation of the controlling shareholder＇s control rights and cash-flow rights. 4） When the controlling shareholder cannot do tunneling, even the interest of minority shareholders still suffer the damage caused by the conflicts of interest between the shareholders and the mangers, but in equilibrium, the minority shareholders would entrust all their wealth to the controlling shareholder, and consequently in this case the corporate