A large number of out-of-step separation devices are installed in the tie lines and power plants near the AC transmission section of Guangxi and Guangdong (Guangxi-Guangdong section), and their reliabilities are very important for the security and stability of the main grid of China Southern Power Grid. Based on the actual primary system, this paper constructs an equivalent system model which can accurately locate the oscillation center and calculate the minimum voltage at the measuring point. Dynamic real-time simulation is carried out for various types and different principles of out-of-step separation devices. Typical problems such as unreliable out-of-step locking criterion in fault process and device refusing to move when the oscillation center is located at the device installation point are found and solved at the same time, based on the power grid panoramic simulation test technology and the actual configuration of out-of-step separation devices, the problems existing in the coordination of out-of-step devices near the Guangxi-Guangdong section are comprehensively studied, and the suggestions of putting the wide area out-of-step separation system into operation as soon as possible are put forward. The improvement and optimization measures proposed in this paper have been applied to the actual system.