The invention provides a voltage reactive-power unified compensator and a control method and a control system of the compensator. The voltage reactive-power unified compensator comprises a series transformer, a shunt transformer, a first antiparallel thyristor group, a second antiparallel thyristor group and a compensating capacitor, wherein the quantity of the antiparallel thyristors in the first antiparallel thyristor group and the quantity of the antiparallel thyristors in the second antiparallel thyristor group are both identical with the quantity of secondary windings of the series transformer. The low-cost devices such as the thyristors, the transformers and the capacitors are adopted to reduce the system cost; all the devices are low-voltage regular components with smaller manufacturing difficulty and high reliability; meanwhile, the structure is simple; the winding quantity of the shunt transformer and the number of the antiparallel thyristors of the antiparallel thyristor groups can be changed to increase the voltage and the reactive power compensating gears, so as to improve the compensating precision; and the compensator can be widely applied to urban and rural power distribution networks.