Abstract: In order to improve the application of frequency scanning method to study sub\|synchronous oscillation (SSO), the basic principle of frequency scanning method is introduced firstly, and its two realization methods are analyzed. Then analysis shows that the series method has relatively wide applications, which can better reflect the nature of frequency scanning method, while the shunt method is more suitable for single\|machine infinite\|bus system without any equivalence calculation. In the end, by the tool of PSCAD, simulation results of IEEE First Benchmark system show that the system equivalence used in frequency scanning method can reflect resonance frequency factually, and both series and shunt methods can be applied to sing\|machine and infinite\|bus system. The simulation results of IEEE Second Benchmark system show that series method can be applied to analyze the SSO of multiple machines system.