Observing the practical shift of national supervision power at the grassroots level from the county level, and exploring the tension between national power supervision and the response of the county system. Based on the case experience of T County, an analysis is conducted around the correlation between county supervision mechanism and governance mechanism. It is found that, on the basis of complying with national supervision discourse, the main functions of county supervision power are expanded, supervision cooperation is embedded, and supervision results are diversified, which is the reconstruction and optimization of the county system on the grassroots supervision system; Relying on institutional authority, the focus of supervision has expanded from the party's discipline and special responsibilities to the central work responsibility of county-level generalization, and highlighted the supervision of power subjects in the process of policy implementation. The practice of supervisory power has been highlighted in the operation of the county-level system, which means that the county-level system has expanded the connotation of grassroots supervisory power while following the national political discourse. By relying on differentiated and integrated supervisory mechanisms, grassroots supervision has become normalized and procedural, and county-level governance has shown a trend of "governance through supervision".