Taking the improved small and medium sized market established and disclosed by the internal audit system as a research object and using Debo internal control index to measure the quality of internal control, this paper makes an empirical research on the influence of internal control characteristics on the level of internal control quality and the changes of internal control quality, from such aspects as the scale of internal audit department and the professional competence of internal audit directors. The result shows professional competence of CAE can significantly improve the quality of internal control. After the relevant examinations, this conclusion remains robust. This indicates that CAE expertise has played an important role in refining and improving the quality of internal control. But the result has not found that the characteristics of the internal audit scale has a significant impact on the level of internal control quality and improvement.