Due to the interaction between power electronic equipment and AC network, the wind-thermal-bundled sending system may cause subsynchronous electrical oscillation, even lead to torsional vibration of the shaft of thermal power units. In order to study this phenomenon in depth, the principle of subsynchronous oscillation of wind-thermal-bundled sending system is firstly analyzed. Then, based on the parameters of a practical regional power grid, 500 kV and 220 kV power grid model including thermal power, wind power and HVDC power transmission is built in PSCAD. The shaft torsional vibration of thermal power unit is excited under specific conditions, which may be caused by subsynchronous harmonic current in wind farm. Finally, the necessary condition of shaft torsional vibration of thermal power unit is analyzed, and the influence of line harmonic impedance, oscillation frequency, line overhaul mode on harmonic current propagation path is simulated and analyzed. This work is supported by Science and Technology Project of State Grid Corporation of China (No. SGJS0000DKJS 1800254) “Research on Key Technologies for Closed Loop Verification of Power Grid Stability Control Function” and Fund of State Grid Shanxi Electric Power Company “Simulation Analysis and Control Measures of Sub-Synchronous Oscillation in Shanxi Power Grid”.