The professional opinion on the audit reports are valuable to those related to the financial market. The CPAs have their social responsibilities and they also must maintain good relationships with their clients. Under these requirements, in their practice, how to maintain independent status is the auditors' major consideration. At what degree can the CPAs, facing with the pressures from clients, general investors, and government, maintain their independence is a problem worthy of investigation. Whether from theoretical or practical point of view. The purpose of this study is to make a primary investigation to the effect of auditors' professional opinion on the financial market. Theoretically, the greater the effect, the greater the pressure CPAs should face, and the more difficult for the CPAs to maintain their independence. According to this study, probably the general investors would react indifferently the first time whether it's a qualified opinion or an unqualified opinion; however, when more and more qualified opinions appear successively, there maybe significant unfavorable effect on the stock price. Furthermore, we can not exclude the possibility of defensive accounting. Ample notifications of their intensions have been given by government and investors. It's time for the CPAs to face the challenge. Owing to the lacking of data in Taiwan, the source of this study comes most from the U.S. Security market. But I believed that the result of this study can be useful to the well-development of our capital market.