The invention discloses an EEAC (extended equal area criterion)-based transient stability critical power transmission section identification method and belongs to the power system and power system automation technical field. According to the method, fault screening is performed on a predicted fault set based on EEAC quantitative evaluation results; candidate section composition branches are screened through using the power fluctuation amplitude of each line in the dynamic process of transient stability simulation; the breaking of the candidate section composition branches is simulated, a node where a dominant complementation group set is located is adopted as a root node, all nodes connected with the root node are traversed, and the subordinate groups of the nodes are marked; nodes in the head nodes and tail nodes of candidate branches, which belong to an S group and an A group respectively, are adopted as starting points and terminal points, all communicated paths connected with the starting points and terminal points are obtained through topological searching; and branches with large power fluctuation amplitude are preferentially selected from candidate branches belonging to the communicated paths so as to form a cut set section. With the method of the invention adopted, requirements for online safety monitoring on a transient stability critical power transmission section under a predicted fault situation are satisfied with the current operating condition of a power grid satisfied.