The invention discloses an automatic sand discharging device and a sand discharging method thereof. The automatic sand discharging device comprises a sand storage hopper used for storing molding sand, a sand box used for product modeling, and a modeling table used for fixing the sand box. The automatic sand discharging device further comprises a control mechanism used for controlling the integral operation of the device, a sand conveying mechanism which is arranged below the sand storage hopper and used for conveying the molding sand, and a sand discharging mechanism which is arranged above the sand box and used for discharging the sand. The sand discharging mechanism is arranged below the sand conveying mechanism and matched with the sand conveying mechanism. The sand conveying mechanism is hung below the sand storage hopper through a hanging assembly and matched with the sand storage hopper. The sand discharging mechanism is fixedly connected with the sand storage hopper. By means of the automatic sand discharging device and the sand discharging method thereof, the production efficiency and yield are improved; meanwhile, the sand discharging amount can be accurately adjusted and controlled every time of processing, the molding sand is effectively prevented from being wasted, and the production cost is reduced.