Taking A-share listed companies from 2008 to 2020 as samples, using the regression discontinuity method, this paper examines the influence of compulsory enforcement of cumulative voting system on benefit encroachment by controlling shareholders. Furthermore, the interaction between the cumulative voting system and the level of equity free cash flow on tunneling behavior is investigated. The findings are that the cumulative voting system can significantly inhibit benefit encroachment by controlling shareholders, the cumulative voting system improves corporate governance and protects the interests of minority shareholders through balance mechanism, defenses mechanism and precautions mechanism. Further research shows that free cash flow of equity plays a moderating role in the cumulative voting system's resistance to tunneling. The implication is that the cumulative voting system enforces policy has certain rationality, which should be adhered to and further implemented.