The invention discloses an aquatic fruit and vegetable juice anti-oxidation composite beverage and a preparation method thereof, and belongs to the technical field of food processing. In the method, four types of aquatic plants, such as water chestnut, gorgon fruit, lotus seed and arrowhead are used as raw materials and water is used as a solvent. The preparation method comprises the following steps: degrading the raw materials by using a biological enzyme and extracting anti-oxidation active substances in the water chestnut, gorgon fruit, lotus seed and arrowhead; and adding white granulated sugar, citric acid, xanthan gum and mineral water into a water extract to prepare a yellowy and clear composite beverage. The composite beverage integrates four types of fruit and vegetable extracts and uses the water chestnut with low price as a main raw material. A product highlights fresh and delicious flavor of the water chestnut, overcomes the defects of poor flavors of the gorgon fruit and lotus seed, has high content of nutrition components, high bioactivity and effects of relaxing bowel, promoting urination, clearing lung and eliminating phlegm, resisting oxidation and the like, and is an excellent beverage which is good for both children and adults.