Abstract: The large-scale development of power system load and power supply installed scale will intensify the power flow exchange between regional grids. In order to improve the economic and reliable power supply capacity of regional power grid, this paper puts forward a potential evaluation method for 220 kV lines considering the power supply capacity of regional power grid, calculates the power flow transfer ratio and power flow sensitivity of key lines after N-1 failure, and calculates the maximum power supply capacity of regional power grid when the key lines are used as bayonet factor. Then, the potential exploitation evaluation index of line transmission capacity is introduced to evaluate the unit transmission capacity of transmission lines in improving the transmission capacity, and to evaluate whether different key lines need to carry out potential exploitation of transmission capacity, so as to provide a more scientific basis for grid planning and construction.