In order to achieve a more accurate power system emergency control measures, this paper proposes a method for calculating the amount of generation tripping considers inertia time constant change and allocates in accelerating generators. The method is based on the equivalent relative kinetic energy in the double-machine system, it does not depend on the specific model and power system parameters, can achieve real-time control of the power system, and needs a small amount of calculation, which is convenient and flexible. Taking the change of system inertia time constant into account in the process of generation tripping, a more accurate generation tripping measure is achieved. Simulation on the New England 10-generator 39-bus system verifies the effectiveness and a certain practical engineering value of the proposed scheme.