In the past, parameter identification of power system was based on the node data, and generator parameters and load parameters were identified separately. Recently with the increased application of the wide-area measurement system (WAMS), the wide-area power system parameter identification has generally become possible. According to the requirement of the wide-area power system modeling, this paper proposes a new thought to identify parameters of the generator and load model at the same time. The identifiability of the generator and load model parameters can be analyzed by the phase’s relation of the trajectory sensitivities. The difficulty of parameter identification can be analyzed by the magnitude of the trajectory sensitivities and the key parameters can be determined. With BPA software and the ant colony algorithm, the parameters are identified and the results are compared for different faults of test system. The feasibility of simultaneously identifying parameters of the generator and load model is verified.