On the basis of the analysis of the related data of A share listed companies from 2008 to 2012 and the study of the influence of the conversion of accounting firms on audit quality, the research shows that the audit quality of accounting firms with special partnership is higher than that of the limited liability; the audit quality of accounting firms after the conversion is higher than that before the conversion; but there is a certain extent of hysteresis effect between the conversion of accounting firms and the improvement of the audit quality. Therefore, the research provides the evidence to support the rationality of the policy of the conversion of big sized accounting firms and provides a certain experience for the necessity of the reform for other small and medium sized accounting firms.