The invention discloses a power system stability control method and system based on a branch potential energy method. The control method comprises the steps that after a power system is disturbed andunstable, a critical branch is searched; the phase angle difference between two ends of the critical branch reaches a commutation sequence threshold; the critical branch is disconnected; whether the disconnected critical branch constitutes a cut set is judged to acquire a judgment result; when the judgment result indicates that the disconnected critical branch constitutes the cut set, the disconnected critical branch is subjected to commutation sequence and then closing; whether the power system is stable is determined; If the power system is stable, stable control of the power system is completed; and if the power system is not stable, the branch is continued to be searched. According to the invention, the stability of the system is restored, and the integrity of the system is maintained; and the energy efficiency and safety of the power system are greatly improved.