In the face of increasingly complex social governance tasks, the traditional bureaucratic government has shown deficiencies in dealing with difficult, trans-boundary issues, which urgently needs to be supplemented by institutional innovation adapted to the current governance scene in China. This paper explores the characteristics and governance mechanism of the leadership alliance system by taking the settlement of the outstanding cases of the VETERANS Affairs Bureau in Q City L District as the starting point. It is found that the Leadership Coalition System has the institutional characteristics of reverse transmission of governance responsibility, upward transmission of governance tasks, and political potential energy to social governance. Together with Pressure System, it forms a closed loop system of upward and downward transmission of governance pressure, ensuring stable and controllable governance pressure at the grass-roots level. It expands the governance capacity of grassroots government departments by relying on the responsibility mechanism of "layer upon layer", the information mechanism of "direct access to grassroots", the organizational mechanism of "upper and lower consultation", the resource mechanism of "coordination and redistribution" and the fine mechanism of "one case and one policy". The leadership alliance system is an institutional channel for the superior leaders to participate in grassroots governance, which provides a new perspective for observing and understanding the logic of Local governance in China.