We take Mainland-Hong Kong Stock Market Exchange Mechanism (hereinafter referred to as Mainland-Hong Kong Stock Connect) as quasi-natural experiment, and use data from A-share listed companies from 2009—2020 to examine the relationship between capital market opening and the degree of tone management. We find that Mainland-Hong Kong Stock Connect has a significant inhibitory effect on tone management, improving the quality of information disclosure effectively.Further analysis shows that its mechanisms lie in improving information transparency, improving corporate governance and easing financing constraints, and the policy effect is more obvious in companies with active funds in Hong Kong. This paper not only expands the relevant research on the influencing factors of tone management, but also provides a theoretical basis and policy reference for the government to further promote a new round of high-level capital market opening.