The invention discloses an electric power system optimal support set positioning method based on anticipated fault decomposition. In order to stabilize the frequency of a power grid, multiple units having decisive effects on safety and reliability of the power grid need to be selected. The method comprises steps of by considering different anticipated faults of the power grid, establishing an electric power system safety restraining optimal power flow mode by taking the minimization of the climbing ability of generator sets as an objective; adopting an anticipated fault decomposition method to decompose the model into a main problem under a normal operation mode and sub problems under each anticipated fault operation mode; through iteration solving of the main problem under the normal operation mode and the sub problem under each anticipated fault operation mode, achieving solving of above electric power system safety restraining optimal power flow mode; and according to the steps, solving the smallest climbing ability transformation quantity of the generator sets, carrying out progressively decreased ranking on the generator sets with the non-zero transformation quantity and successively recording the generator sets to be the optimal support sets with progressively decreased priorities according to the sequences to be output as the results. The method is excellent in applicability and actual requirements are well met.