The invention discloses a double-protein fermented milk beverage rich in active Lactobacillus plantarum and a preparation method thereof, and belongs to the technical field of fermentation engineering. The preparation method includes the following steps: inoculating Lactobacillus plantarum into double-protein base material components with the addition of proliferating factors and inorganic salts for fermentation to obtain fermented milk, and then adding stabilizers, sweeteners and water into the fermented milk for blending to obtain the fermented milk beverage; the preparation method can successfully realize the proliferation and fermentation of the Lactobacillus plantarum in the double-protein base material, and can greatly shorten the fermentation time of the Lactobacillus plantarum in the double-protein base material; the fermented milk beverage obtained by the preparation method is high in probiotic content, and the viable count can reach 5.0 x 10 8(superscript) cfu/mL or above; regarding the fermented milk beverage, the product system is stable, the protein content meets the requirements of national standards, sourness and sweetness are palatable, and the cost can be controlled; and the fermented milk beverage obtained by the preparation method is performed with low temperature storage at 0-10 DEG C for 21 days, and the viable count can be stabilized at 3.0 x 10 7(superscript) cfu/mL or above.