The invention discloses a lactic acid bacteria beverage and a preparation method thereof. The lactic acid bacteria beverage is prepared from 0.5%-5% of fermented milk base stock, 0.2%-0.9% of milk protein powder, 0.15%-0.4% of soluble soybean polysaccharide, 0-0.2% of pectin, 0-0.1% of soluble sodium salt, 7%-10% of sweet substance, 0.05%-0.2% of acidity regulator and the balance water. The preparation method comprises the following steps that 1, the water, the milk protein powder, the sweet substance, the soluble soybean polysaccharide, the pectin and the soluble sodium salt are mixed to be uniform, and then sterilizing and cooling are conducted; 2, the obtained mixture and the fermented milk base stock subjected to sterile homogenizing are mixed to be uniform; 3, the obtained mixture and a mixed solution of the acidity regulator and the water are mixed to be uniform, sterile homogenizing is conducted, and the lactic acid bacteria beverage is obtained. The prepared lactic acid bacteria beverage is low in protein, low in sugar, appropriate in sourness and sweetness and fresh and cool in mouthfeel, the stability can be maintained within the guarantee period, and the phenomena of water separating, layering and precipitating do not exist.