After synchronous condenser being put into operation as the match project of UHVDC transmission, it’s reasonable to investigate its influence on the operation of large-scale AC-DC hybrid grids, as well as explore its control strategy. Firstly, this paper researches the reactive power characteristics of condenser and builds its reactive power supporting models for different time scales. Secondly, simulations are carried out with the East China Power Grid, the condenser’s influences on voltage characteristics, short-circuit current and commutation failure characteristics are analyzed. The result reveals that condenser could considerably enhance the voltage supporting capability, improve the power grid strength and decrease the risk of UHVDC commutation failure. The validity of theoretical analysis is also verified by the simulation. Finally, a unified dispatch strategy which adopts small difference coefficients and steady lagging-phase operation is proposed for integrating the condenser into AVC system. By adopting the proposed strategy, condenser’s dynamic reactive power supporting function can be sufficiently utilized. This work is supported by National Natural Science Foundation of China (No. 51607092).