Abstract: Voltage source doubly fed wind turbines have attracted widespread attention for their ability to establish and support voltage. However, doubly-fed induction generator (DFIG) controlled by voltage sources are more likely to cause shaft torsional vibration problems and even deteriorate torsional damping in response to grid dynamics. Therefore, this article analyzes the damping characteristics of shaft torsional vibration from the perspective of energy dissipation and proposes a quantitative characterization method for shaft torsional vibration damping. Firstly, a transient energy function of the shaft system was constructed based on a two-mass block transmission model of the shaft system. On this basis, the potential energy and dissipated energy of the shaft system were extracted to characterize the accumulation and dissipation effects of energy during the oscillation process of the shaft system, and the relationship between energy dissipation and the real part of the eigenvalues was explored; Analyzed the influence of different virtual synchronous generator (VSG) control parameters on the torsional damping characteristics of the shaft system; And an energy dissipation factor was defined to characterize the damping of shaft torsional vibration quantitatively. Finally, simulation verification was conducted on the conclusions and methods proposed in this article.