The invention discloses a composite fermented beverage and a preparation method thereof, and belongs to the technical field of fermented food processing. A formula of the fermented beverage, comprises, by mass, 45-60 parts of walnut meal, 10-20 parts of pseudo-ginseng, 2-5 parts of medlar, 2-5 parts of jujube, 3-6 parts of yam, 2-3 parts of ginger, 300-500 parts of drinking water, 3-6 parts of honey, 0.2-0.4 part of lactobacillus starter and 8-10 parts of oligofructose. The walnut meal and pseudo-ginseng mixed fermented beverage not only retains the unique flavor of the pseudo-ginseng but alsohas the pleasant lactic acid flavor after fermentation and can be obtained after fermentation for 20 days, and the time is short. The fermented beverage has soft taste, moderate sweet and sour tasteand rich nutrients. The beneficial bacteria fermentation process is simple and safe, and products are healthy. The composite fermented beverage has the functions of oxidation resistance, blood pressure lowering and blood fat lowering.