Abstract: In order to study the influence of rotor damping winding on the transient reactive power characteristics of synchronous condensers, this paper takes a synchronous condenser as an example to build field-circuit-grid coupled time-stepping finite-element model to calculate the electric quantities of synchronous condensers including the reactive power and stator and rotor currents, and compare and analyze the influence of damping and non-damping on the electric quantities; on this basis, the influence of different materials of damping winding including copper, aluminum and stainless steel on the transient reactive power characteristics of synchronous condensers is studied. The results show that rotor damping winding could improve obviously synchronous condenser reactive power support capability and suppress excitation overcurrent; when damping winding is made of copper, the synchronous condenser reaches the optimal reactive power characteristics. The research results provide technical support for the reactive dynamic characteristics of synchronous condensers and further guarantee the stable operation of the power grid voltage.