The invention relates to oil well completion equipment, and particularly discloses a cluster ash discharging tank type movable skid-mounted cement mixing system, which is characterized by at least comprising a movable skid-mounted storeroom, a compressor, a ground storage tank and vertical ash discharging tanks; a mixed material is stored in the movable skid-mounted storeroom; the vertical ash discharging tanks have a cluster structure; each vertical ash discharging tank is provided with an ash inlet valve, an air inlet valve and an ash outlet valve; the ash inlet valve and the ground storage tank of the movable skid-mounted storeroom are in branch connection through a pipeline; the feeding and discharging control for all the vertical ash discharging tanks is realized by controlling the opening and closing of valve gates of each ash inlet valve and each ash outlet valve; the vertical ash discharging tanks are vertical tanks with self-weighing capacity, and are fixedly connected with aground foundation supporting base through 3-4 supporting arms; and the middle part of the supporting arm is connected with a weighing device for weighing the weight of the material entering the vertical ash discharging tanks and controlling the weight of the material discharged from the vertical ash discharging tanks. The system implements automatic treatment of receiving and discharging, conveying, mixing and stirring, and loading, and meet the requirement of simultaneously mixing and stirring various oil well cement additives and admixtures.