When the permanent magnet synchronous generator is connected to the weak AC system,the subsynchronous oscillation problem will be caused.A Taylor expansion was performed on the equivalent impedance transfer function of the power system,and a quantitative calculation of subsynchronous oscillations when the permanent magnet synchronous generator was accessed to a weak AC system was proposed.The whole system mathematical model was established according to the characteristics of the permanent magnet synchronous generator connected to the weak AC system.The equivalent impedance of the whole power system was calculated.The Taylor expansion was performed based on the equivalent impedance transfer function,and the characteristics of the Taylor expansion were analyzed.The damping and frequency of the synchronous oscillation were calculated quantificationally.Finally,in the MATLAB/Simulink software,the validity and accuracy of this method were tested by time domain analysis.