Accurately detecting the properties of low-frequency oscillation is important to suppressing power system oscillations and reducing its harms during a low-frequency oscillation.By an analysis of the characteristics of low-frequency oscillation curves with different mechanisms，this paper presents an oscillation property identification method based on envelope fitting.Firstly，the dominant mode oscillation curve of the vibration signal is extracted by the empirical mode decomposition（EMD）method.Then the envelope of the dominant mode signal extracted is fitted.Based on the fitting error，the properties of oscillations are determined.The process and the realization method for property identification are given.The validity of the method proposed is verified through both simulation data and actual data recorded by the wide area measuring system.