Abstract: The application of grid-forming control (GFM) to wind turbines is an effective technical means to alleviate the frequency and voltage stability problems of power systems with high proportion of new energy. Currently, research predominantly focuses on the grid-side characteristics of grid-forming wind turbine (GFM-WT), whereas insufficient attention has been focused on the potential electromechanical coupling interaction characteristics. Specifically, GFM greatly enhances the dynamic interaction between the grid and the drivetrain of GFM-WT, which means that drivetrain torsional vibration can also be stimulated by perturbation from the grid easily. To investigate the drivetrain torsional vibration characteristics of GFM-WT and damping the torsional vibration, the state-space model of GFM-WT considering the electromechanical coupling characteristics is established first. Then, by utilizing eigenvalue locus analysis, the necessity of introducing additional torsional vibration damping control for GFM-WT is demonstrated. The mechanism behind the limited application of traditional drivetrain torsional vibration damping method (TDTVD) in GFM-WT is explored. On this basis, a drivetrain torsional vibration damping method based on the virtual synchronous phase angle compensation (VSPAC) is proposed, which effectively solves the problem of under-damping or even vibration divergence of the GFM-WT's drivetrain. Finally, the theoretical analysis results and the efficacy of this proposed method are validated by the Bladed + NovaCor co-simulation real-time platform.