The invention provides a fermented soymilk beverage. In terms of a total weight of 100 weight parts, the fermented soymilk beverage comprises the following raw materials: 3-10 parts by weight of soybean, 0.5-15 parts by weight of white granulated sugar, 3.0-9.0 parts by weight of reducing sugar, 0.21-0.65 parts by weight of a thickening agent and 0-0.20 parts by weight of an acidity regulator. The fermented soymilk beverage is prepared by soybean slurry grinding, batching, browning and fermentation. The thickening agent includes pectin, arabic gum and gellan gum, and is added after fermentation. The invention also provides a preparation method of the fermented soymilk beverage. The fermented soymilk beverage product system provided by the invention is uniform, and almost has no floating, precipitation or stratification phenomenon when it is placed at room temperature.