Abstract: The parameter identification of subsynchronous oscillation based on synchrophasors can effectively monitor the dynamics of subsynchronous oscillations. This paper proposes a real-time parameter identification method for subsynchronous/supersynchronous oscillations in power systems based on synchrophasor trajectory fitting. The frequency, amplitude, and phase of the frequency-shifted fundamental, subsynchronous, and supersynchronous components can be accurately obtained by solving the overdetermined nonlinear synchrophasor trajectory fitting equations. By utilizing the trajectory characteristics of the coupled rotation of the synchrophasor's positive and negative frequency parts corresponding to each component, this method can perform real-time parameter identification only based on the 100ms synchrophasor data sequence. Compared with the existing algorithms, the proposed method has the following advantages: on the one hand, it can identify the parameters of the supersynchronous component coupled with the subsynchronous component. On the other hand, the extra short data window greatly improves the real-time performance of the algorithm and overcomes the frequency resolution limitation of the spectrum analysis method. The comparative analysis results with simulated phasor measurement unit(PMU) data and actual simulation data show that the proposed method can accurately obtain the fundamental and subsynchronous/supersynchronous parameters and effectively realize the real-time dynamic monitoring of subsynchronous oscillations.