The invention discloses a method for fault component-based wide area backup protection, which belongs to the field of relay protection for electric power systems. The method comprises the following steps of: when a power network is in normal operation, dividing protection associated domains according to a topology structure and the PMU configuration of a network; updating the protection associated domains in real time by adopting a heuristic search technique according to switch transposition information; when a fault happens, extracting fault stable-state components of current and voltage, and defining fault associated domains according to the fault stable-state component of differential current in each associated domain; and calculating fault associated factors in the associated domain in real time to determine fault branches. The method can accurately position the faults under a condition with PMU limited measuring points, is not influenced by the system operation mode, avoids the condition that the conventional backup protection can have mismatching or insufficient sensitivity very easily, is not influenced by load current, and has very high reliability.