The invention relates to a sludge treatment method and a system thereof, and especially relates to a method for treating the sludge in waste water from the alumina production process and its system. The treatment method comprises the following steps: the separated sludge from waste water is conveyed to a sludge mixed pool, and conveyed to a red mud storing groove by a transfer pump during the alumina production process, sludge in the red mud storing tank and the filtered red mud are stirred and mixed, and conveyed to a red mud stockyard by an efflux pump for storing. The invention has the advantages that a series problems, such as complex flow and high energy consumption, of a traditional sludge processing method which needs additional equipments and needs addition of polymer can be solved, the equipment investment can be reduced, the investment cost of the alumina factory can be decreased, the sludge treatment flow can be shortened, the operation cost is reduced, and the sludge conveying and possible stocking problems can be solved, the manpower and the material resources can be saved, and the effects of energy saving and emission reduction can be reached.