Abstract: Under the impact of large disturbances, the rotor angle stability information is contained in the response of both the generator cluster and the network. In this paper, the voltage phase of the network nodes at different spatial positions during rotor angle swing has the characteristic of "group belonging" is revealed firstly, and the voltage phase difference between the nodes at both ends of the critical branch is consistent with the rotor angle difference of the generator cluster. For the branch transient transmission capability (BTTC) method based on the network response and the extended equal area criterion (EEAC) method based on the generators' response, the correlation and difference between the two methods of rotor angle stability evaluation and the technical complementarity of the two methods in dividing the group of coherent generator cluster and determining the critical index are systemically analyzed. The simulation results show that the BTTC method can be used for EEAC method to quickly partition the group of co-shunting generators, EEAC method can provide an unstable equilibrium point for BTTC method to determine the critical stability index.