After system faults are cleared， trajectory eigenvalues can be calculated along the system trajectory. The sensitivities of the eigenvalues to the power injections are deduced. Control sensitivities of different generator nodes are defined and obtained quantitatively accordingly. They can be used to determine the location of emergency control and allocate the amount of load shedding. The algorithm provides control locations quickly， which is suited for formulating the control strategy. Case studies on the New England 39-bus system and an actual domestic power system are provided to demonstrate the approach. The results show that the proposed approach can maintain the system stability effectively.