A throwaway dog's dung bag and adjustable tie-belt combination unit includes a throwaway bag and tie-belts for fixing the bag on dog's buttocks, wherein the bag is a soft sack with hard frame on its mouth. Hook rabbets are provided on the two flanks of the frame. A vertical tie-belt is fixed to surround dog's abdomen or legs. Two horizontal tie-belts, one end of which is separately connected to the two flanks of the vertical tie-belt, while the free end of which has hooks for hooking into the rabbets in bag frames. Thus, the bag can be fixed to the dog's buttocks. The opening of the frame is placed against dog's anus to receive excreta. Such unit can enhance environment protection and sanitation conditions.