With the data of A-share listed companies with mandatory rotation of CPA in Shanghai and Shenzhen Stock Exchanges from 2003 to 2017 as research sample, this paper studies the effect of reappointment on audit quality and the adjustment effect from accounting firm size,and examines the differences of the adjustment effect among listed companies with different financial conditions.The results show audit quality is reduced due to the reappointment of CPA after mandatory rotation. Large-scale accounting firms can effectively reduce the effect of the reappointment of CPA on the audit quality.Compared with the companies with better financial conditions, the regulating role of firm size in the companies with worse financial conditions is more significant.The conclusion of the study can provide experience support and value reference for improving the rotation mechanism of CPA and strengthening the supervision of CPA industry.