Abstract: Aimed at the problem of power system low frequency oscillation, based on analyzing of oscillation mechanism and oscillation characteristics with single-machine infinite bus system, this paper proposed an improved HHT algorithm using end optimization symmetric extension method to identify modal parameters of power system low frequency oscillation. Through simulations with testing signal and restraining experiments utilizing wide-area FNET measurement system, the paper also analyzed the effectiveness and veracity of the proposed algorithm. Simulations and experiments showed that the low-frequency oscillation pattern information can be effectively identified based on the proposed HHT algorithm. At the same time, the proposed method is also proved to have a good help to guide the disposition and parameters’ design of power system stabilizer, thereby the safety and stabilization of power system are maintained.