Abstract: A thermal cooker having high insulating efficiency and capable of boiling and smothering food is provided. A thermal storage ring is connected to an outer bottom surface of an inner pot of the thermal cooker to be heated along with food in the inner pot until the food is boiled. The inner pot with boiled food and heated and glowing thermal storage ring is then positioned into an outer pot and closed with inner and outer lids, so that food in the inner pot is kept boiling with heat released from the thermal storage ring and then be smothered in the thermal cooker for a period of time.