Abstract：Based on signal theory and agency theory of auditor, this paper empirically study the relationship between auditor and the change of committed investment projects using the data from 2000 to 2011 in Chinese listed firms. The conclusions of the paper are: (1) During IPO period, high auditing quality can sign lower risk of investment orientation changes, and support the signal effect of auditor. (2) Further research found that, among the companies that did not change auditor during past three year of IPO, those who employed high auditing quality had a lower rate of investment orientation changes than other companies. (3) Those who employed high auditing quality will take obvious change more than that of concealed change. These results show that the high auditing quality in the capital markets can play the role of audit external governance, and reduce agency costs, protect the interests of investors.