A mouth-opening training device includes a water-filled bag having a zigzag edge or a sawtooth edge. By increasing or decreasing the amount of water located inside the water-filled bag to alter the total thickness of the water-filled bag, said device can accommodate different thickness of occlusion of teeth of a patient. Said device can make a further improvement on layers of flavor in occlusion of the teeth. Said device can further include a plurality of pivotable plate-shaped objects connected or coupled to the water-filled bag. The plate-shaped objects can provide different thickness combinations and further meet the user demands on thickness of occlusion of the teeth.
