The present invention provides a wide-area backup out-of-step solution determination method based on an out-of-step oscillation characteristic set. The method comprises the steps of (1) applying the object analysis based on an out-of-step solution criterion of the out-of-step oscillation characteristic set; (2) applying the target analysis based on the out-of-step solution criterion of the out-of-step oscillation characteristic set; (3) applying the range analysis based on the out-of-step solution criterion of the out-of-step oscillation characteristic set; (4) extracting the characteristics of an out-of-step oscillation set based on the out-of-step solution criterion of the out-of-step oscillation characteristic set; (5) obtaining a wide-area backup out-of-step solution criterion based on the out-of-step oscillation characteristic set. According to the present invention, an out-of-step oscillation situation that an out-of-step oscillation center drops at a power grid non-preset solution position is accorded effectively, three requirements for the out-of-step solution measures of three lines of defence in the electric power system safety and stability guide rules are realized, and the conventional insufficiency based on the situ amount solution measures is made up.