The paper analyzed the application of complex torque coefficient (CTC) approach based on the IEEE 2th benchmark of SSR. It deduced mechanical and electric CTC, and studied the influence of unstable model outside the shaft. If there is no unstable model, the CTC can be computed just by the transfer function. Otherwise, there is no rigid CTC, and additive simulations are needed to verify the analysis results. The study shows, the models of generators have obvious influence on the CTC characteristics and system stability, the multi-mass and single mass model is more exact and the fixed frequency source models will lead to some errors.