The invention belongs to the technical field of feeding equipment for a ball mill in a concentration plant, and in particular relates to a belt ball adding underground ball feeding device for the ball mill. The device comprises a ball feeding bin, a ball discharging device and a ball mill control box, wherein the ball feeding bin consists of a funnel-shaped bin body, a steel rail layer and a ball outlet; the ball discharging device consists of a fan gate, an electric push rod device, a steel ball belt conveyer and a steel ball weighing scale; the electric push rod device, the steel ball belt conveyer and the steel ball weighing scale are connected with the ball mill control box; the ball mill control box is provided with a steel ball weighing display screen and a control button; and the steel ball weighing scale is connected with the steel ball weighing display screen. The device is reasonably configured, has a compact structure, a high automation degree, small maintenance amount and a high operating rate, saves cost, does not occupy ground space, and is favorable for ensuring the smooth proceeding of production.