The invention relates to a combination converter control method and system thereof for supplying power to passive system, wherein the combination converter is composed of N basic converter units through being in series and boosting pressure, and utilizes MCC as the basic converter units. The N-1 basic converter units of the combination converter utilizes constant dc voltage control, the N basic converter unit utilizes constant ac voltage control; the positive sequence reactive power current instruction generated by the N basic converter unit utilizing the constant ac voltage control is divided into N equal parts, the N equal parts are respectively utilized as the positive sequence reactive power current instructions of the N basic converter units in the combination converter. The control method has the advantages that the Dc voltage balance and power sharing of the basic converter units in series in the inner of the combination converter are guaranteed under the circumstance of normally supplying power to passive system, and the quick configuration and restart of the whole combination converter control strategy are conveniently realized after the basic converter units are broken.