The invention discloses a concrete quantitative stirring device for construction machines. The concrete quantitative stirring device for construction machines structurally comprises a valve controller, a discharging head, a valve plate, a leakage-prevention device, a base, a first draw-off pump, a second draw-off pump, a stirring motor, a conveying pipe, a control box, a stirring box and a manualadding opening; the first draw-off pump and the second draw-off pump are locked to the left side of the top end of the base perpendicularly, the stirring box is welded to the top end, the first draw-off pump is located on the front side of the second draw-off pump, and is located on the left side of the stirring box, and electrically connected with the leakage-prevention device, the right end isin glued connection with the upper side of the left end of the control box through the conveying pipe, when the device is used, through mechanisms of a gear, an up pressing plate, a spring, a power connection contact rod and the like of the device, when the discharging opening is opened, raw material draw-off equipment of the device is in the power-failure state, when the discharging opening is closed, the equipment automatically returns to be in the access state, when the device is used, the phenomenon that a user forgets to close the discharging opening is avoided, and therefore leakage of raw material adding is avoided, raw material waste is avoided, and use is convenient.