The invention discloses a successive approximation type load shedding capacity control method based on a power ratio. The method comprises the following steps of 1, setting a constant value Kthresholdof an action threshold ratio for judging whether or not load shedding is needed; 2, calculating a power bearing ratio K of the interoceptive power of a local power grid to the total load power of a local area; 3, when the power grid breaks down and an interoceptive channel of the local power grid is disconnected, judging whether or not load shedding is needed according to the power bearing ratioK before the accident, and when K is greater than or equal to the Kthreshold, carrying out the load shedding measure. By means of the method, the accuracy of calculating load shedding capacity after the interoceptive channel of the local power grid is disconnected can be improved, and conditions are created for detecting grid connection in the same time period.