Abstract: Coordinated control of reactive power compensation is essential to the stability of bus voltage in high voltage direct current（HVDC）connected to weak AC system and characterized with frequent power fluctuation.Based on the coordination of the static synchronous compensator and fixed capacitors,a multi-mode control strategy is proposed,including the steady-state voltage regulation mode,the automatic voltage control（AVC）mode and the transient control mode.In the steady voltage regulation mode,the converter bus voltage can be controlled at its rated value with zero steady-state error by the coordinated control of the static synchronous compensator（STATCOM）and capacitor bank,while the reactive component devices of the HVDC converter will participate in the voltage regulation of nearby power grid in the AVC mode,and the transient control mode is created for mitigating voltage fluctuation and reducing the probability of commutation failure during grid fault period.Besides,according to the actual parameters of the±800kV DC power transmission project from Jiuquan to Hunan,a model is established.Then,different working conditions,such as DC power fluctuation,operation complying with the AVC commands and short-circuit accident are carried out.The correctness and effectiveness of the proposed control strategy are verified by the simulation results.