The invention relates to a method for calculating a transient stability limit value of an electric power system according to the stability index sensitivity, which is characterized by comprising the following steps of establishing a system model under a center of inertia system, an individual machine energy function of a generator under the center of inertia system, and a stability index of the generator based on the individual machine energy function; and calculating the stability index sensitivity. The calculation of the limit value of stable operation of the electric power system by using the method is based on the trajectory analysis method and trajectory sensitivity, and the calculated stability index on the sensitivity of parameters can fully reflect the influence of the parameters on a dynamic system, so that a calculation result of the limit value of stable operation of the electric power system obtained by the method is accurate, and the method is simple and fast; and compared with the existing method, the method is only based on dynamic trajectory of the dynamic system and independent of stability boundary obtained in advance, and the model has strong adaptability and higher application value.