The invention discloses an estimation method of capacity exchange ability between large regional grids of an electric system. The method comprises the steps: based on sensitivity analysis of a section exchange capacity-voltage change ratio, carrying out analysis on the section exchange capacity-voltage stability of a tidal current section between the large regional grids, and obtaining the most sensitive node of voltage of a system; and carrying out spline interpolation on a trend of voltage change to sensitivity change, wherein the voltage change is based on the most sensitive node of the voltage of the exchange capacity, carrying out derivation after nonhomogeneous exponential function fitting is conducted on a discrete value obtained by the spline interpolation, obtaining a change rate function of the voltage change to sensitivity, calculating a limit of the exchange capacity according to discrimination conditions of a critical point of voltage stability, analyzing the voltage stability conditions of the system through a voltage stability margin, and carrying out checking and calibration on correctness of an inflection point and an estimation result of the exchange capacity.