A synchronous camera dynamic reactive power co-control method and system for UHVDC converter station are disclosed, the invention transmits a pre-switching instruction to a synchronous camera throughan ultra-high voltage direct current control and protection system at the time Delta T1 of the first appointed time before the AC filter group is controlled to be switched on and off, and the synchronous camera receives the pre-switching instruction and reduces the reactive power output according to a certain proportion; The reactive power output is increased according to a certain proportion whenthe pre-cut instruction is received. After the AC filter (capacitor) is switched on and off, the synchronous camera is switched to the constant voltage mode, so that the grid voltage is restored to the rated value. The invention can ensure that the inverter station still maintains the constant arc extinguishing angle control, avoid the risk of the voltage sag of the power network exceeding the lower limit, improve the voltage stability of the alternating current bus bar and provide more reliable reactive power support.