The invention discloses an effervescent tablet for improving immunity and a preparation method thereof. The effervescent tablet comprises the raw materials of beta carotene, vitamin B1, vitamin B2, vitamin B6, vitamin B12, vitamin C, vitamin E, pantothenic acid, folate, biotin, zinc gluconate, copper gluconate, yeast selenium, an acanthopanax extract, an astragalus extract, a grifola frondosa extract, a citrus extract, inulin, citric acid, malic acid, sodium bicarbonate, aspartame, food flavor, sodium chloride, PEG6000 and milk sugar, and the raw materials are prepared into the effervescent tablet by a direct powder compression process. The effervescent tablet has the advantages of quickness of absorption and convenience for use, and is used for supplementing vitamins and mineral substances for children, old people, while collars, and the like with hypoimmunity and improving the immunity, and plays a health care effect.