Abstract: The information asymmetry of listed company is an important problem in the process of securities market development. This paper explores the main forms of information asymmetry, such as incomplete information disclosure , timelessliness, forging information, and so on. It also analy-ses the causes and results of information asymmetry. On this basis, it presents the countermeasures of improving internal and external constraint and incentive mechanism of company so as to lower the degree of information asymmetry.