Agency theory, which discusses the conflict between agent and principle, was developed by Jensen and Meckling in 1976. Owing to the separation of ownership and management, shareholders and management authority have agency relationship. The one reason that shareholder hand in company affairs to management authority is that management authority has better management ability. Another reason is that shareholder cannot handle by himself for some reasons and must hand in to other people. Management authority has the advantage of information and they also seek for their own interest. But these behaviors may damage shareholder¡¦s right and agency problems occur in the situation. Agency problems occur not only between shareholder and management authority but also between management authority and lender in a company with debt. Shareholders often supervise management authority more strictly and make more rules to confine management authority in order to reduce agency problem or protect their own interest. But these actions disturb management authority when management authority is full of ambitions and endeavor. If agency problems between shareholder and management authority cannot be solved properly, it will make company operate abnormally and damage the nation¡¦s economic further. On the contrary earning forecast can reduce information asymmetry. If management authority can disclose earning forecast voluntarily, it is helpful to reduce the agency problem and the information asymmetry between shareholder and management authority. The article assumes management authority disclose earning forecast voluntarily in order to get shareholder and debtor¡¦s trust in this point of view and use firm size¡Bfree cash flow¡Bleverage as the proxy of agency cost. In this research we find that the more debt the company have, the higher voluntarily the company discloses earning forecast. It is the same as we expect. But free cast flow is not significant. When firm size is bigger, the management authority is less voluntary to disclose earning forecast. The result is contrary to the view of agency problem.