The opening of the branch offices of “Big 4” accountants in China has restructured Chinese audit market, and its impact on audit quality deserves attention. Based on this, this paper uses the quasinatural experiment of “Big 4” accounting firms opening offices, and takes Ashare listed companies in Chinese capital market from 2008 to 2021 as research samples to examine impact of the opening of branch offices of “Big 4” accounting firms on audit quality and its economic consequences empirically. The research finds that: The opening of branch offices of “Big 4” accounting firms can improve audit quality significantly. By differentiating between firm types and analysts attention, it is found that the promotion of audit quality by setting up branch offices of “Big 4” accounting firms is more obvious in local accounting firms and enterprises with low attention of analysts. Further research shows that the opening of branch offices of “Big 4” accounting firms improves audit efficiency and reduces audit pricing, and has a positive effect on the opening of branch offices by “Big 4”. The conclusion of the research provides empirical data support for the positive effects of “Big 4” accounting firms entering the Chinese audit market, and it also provides theoretical references for the optimization and improvement of Chinas audit market.