The invention relates to an energy storage planning method based on power system transient stability as well as a system. An energy storage access position, output power of a generator as well as amplitude and a phase angle of a node voltage are taken as optimization variables and are input a transient stability risk mitigation model constructed in advance; and according to an objective function and constraint conditions of the transient stability risk mitigation model, an optimal configuration scheme is determined, wherein the transient stability risk mitigation model is constructed on the basis of minimization of energy storage and generator output power costs as well as predefined transient stability risk indicators, and the transient stability risk indicators are developed according tofault severity and fault occurrence probability of an uncertain scene.