Using the unbalanced panel data of companies listed on Shanghai Stock Exchange and Shenzhen Stock Exchange from 2014 to 2018 as a research sample, through empirical analysis, the relationship among institutional shareholder activism, the background characteristics of the audit committee director and the efficiency of the audit committee are studied. The following conclusions are drawn：(1) The reputation level of the audit committee director is positively related to the audit committee effectiveness；(2) The company’s audit committee effectiveness is higher when the chairman of the audit committee is localized；(3) Compared with companies with lower institutional investor shareholdings, in companies with higher institutional investor shareholdings, the reputation level and localization of the audit committee director can improve audit committee effectiveness more effectively；(4) Compared with transactional institutional investors, stable institutional investors can positively moderate the correlation between the audit committee director background characteristics and the audit committee effectiveness.