This paper examines the relationship between industry expertise type, time lag of audit report and audit quality based on A-share listed companies from 2007 to 2018. we divide Accounting firms' Industry expertise into "product" industry expertise, which is formed by auditing a small number of large-scale customers, and "low-cost" industry expertise, which is formed by auditing a large number of small-scale customers. The results show that accounting firms with "product" industry expertise tend to have longer audit time lag and higher audit quality than accounting firms with "low-cost" industry expertise. The result of this research expands the research angle of industry expertise type, and provides the reference for the customer to choose the Accountant firms.