This paper studies the influence of equity balance on the performance of the company from two aspects of investment efficiency promotion and large shareholders’ hollowing down. On this basis, the paper further studies the impact of the large shareholder holding level and the large shareholder relationship on the effectiveness of equity checks and balance. Using the data of private listed companies in China, this paper constructs an empirical research model based on investment efficiency and tunneling as mediator variables. The results show that equity balance improves corporate investment efficiency and inhibits the tunneling of large shareholders, thereby enhancing the performance of the company. Therefore, from the perspective of the second type of agency cost, the effective balance view of large shareholders has been verified. The controlling rights of several major shareholders play an important role in restricting large shareholders’ looting of the company behavior. Equity balance promotes the efficiency of corporate investment, and other large shareholders can also inhibit the tunneling behavior of large shareholders. However, for large shareholders with strong control, equity balance cannot play a corresponding role in corporate governance. In the plundering of the interests of minority shareholders, large shareholders will not only show equity checks and balance, but also collusion between major shareholders. If there is a large shareholder in the company, the possibility of conspiracy to be emptied by the company is relatively large. When the company has many large shareholders and these large shareholders have a hollowing motive, they may join up to act together to form a conspiracy of large shareholders. 　　The contributions of this article lie in two aspects. First, the research on equity balance in promoting the efficiency of investment and restraining the corporate governance effect of large stockholders, explores the effect path of equity balance on the performance promotion, and the related research results of expanding and perfecting equity balance. Second, by studying that major shareholders may form a joint conspiracy to invade the company’s interests and analyzing the impact of the shareholder relationship on the effectiveness of equity checks and balance, this paper reveals the relationship between relational shareholders and equity checks and balance, which affects the company’s performance and tunneling. The conclusions provide a theoretical basis and policy recommendations for the improvement of the company ownership structure, the corporate governance mechanism and the investor protection.