The invention relates to a life-prolonging nutritious gruel and a preparing method thereof. The nutritious gruel is prepared by the raw materials of non-glutinous rice, corn, oat, black sesame, carrots, taros, sweet potatoes, potatoes, cabbages, celtuce, yams, soybeans, horsebeans, black beans, red beans, hyacinth beans, peas, catjang, peanuts, filbert, platycladi seeds, gordon euryale seeds, lily, white lotus seeds, barbary wolfberry fruit, black fungus, white fungus, champignon, tuckahoe, lucid ganoderma, and grapes. The preparation method comprises the following steps of grinding the grains, beans and dried fruits raw materials of the above standby food materials into fine power; adding water for cooking; juicing the carrots, taros, yams, sweet potatoes, potatoes, cabbages, celtuce, peanuts, filbert, platycladi seeds, barbary wolfberry fruit, black sesame, black fungus, white fungus and grapes of the standby food materials and extracting fruit-vegetable fungus juice therefrom; and boiling the extracted fruit-vegetable fungus juice to obtain the life-prolonging nutritious gruel. The invention takes mild-natured food materials as main raw materials which are matched with the fruit-vegetable fungus juice, has reasonable and balanced nutrition, achieves the efficacy of prolonging life in diet therapy, and is particularly suitable for middle and old aged people.