Abstract: China Securities Investor Services Center (ISC for short) is a regulatory minority shareholder with Chinese characteristics. It is of great value to explore the effects of ISC exercising on mitigating the chaos of mergers and acquisitions and promoting the protection of minority investors. Based on major asset reorganizations in which ISC participated in the media briefing from 2016 to 2021, DID model and quasi-natural experiment were used to analyse the protection and spillover effects of ISC exercising. The results showed that: (1) There was a negative market reaction to the exercised major asset reorganizations, and ISC exercising had an obvious warning effect on minority investors. (2) ISC exercising reduced the transaction value-added rate of target assets and mitigated the reorganization problems of high valuation, high premium and high commitment (three highs for short). (3) The warning effects of ISC exercising spilled over to other reorganizations through the connection of independent financial advisers. (4) The mitigation effect of ISC exercising to “three highs” problem spilled over through the connection of asset appraisal agencies and law firms.