Abstract: Serious subsynchronous resonance(SSR) will threaten the operation of power system. An investigation and analysis is made in this paper of the effect of a voltage-source converter (VSC) on sub-synchronous resonance which is installed near the synchronous generator. The equivalent output impedance of VSC, which is made up of a series of circuit components, and its control parameters are the key factors for interactions with the grid. The effect of the equivalent output impedance of VSC on the damping of the system with the complex torque coefficient method is analyzed, and then, the VSC is further improved to increase the equivalent implanted damping resistance and to achieve the damping subsynchronous resonance. The time-domain simulation proves that the VSC impedance adjustment technology can damp the subsynchronous resonance to a certain extent.