Bulgarian Lactobacillus, Streptococcus thermophilus and Lactobacillus plantarum were inoculated into tartary buckwheat seedling beverage for fermentation, and the changes of sensory score, number of live Lactobacillus, total sugar, reducing sugar, total acid, total protein, total flavone, rutin, quercetin and kaempferol 3-rutinoside were compared for the better lactic acid bacteria fermentation strains. The results showed that Lactobacillus could grow well in tartary buckwheat seedling beverage, and the fermentation activity of L. plantarum was higher than that of the other two lactobacilli, and the mixed fermentation of L. plantarum and L. bulgaricum had synergistic effect, and the product sensory score was the highest. The contents of total sugar and reducing sugar in beverage decreased due to the fermentation of different Lactobacillus. After the fermentation for 48 h, the total sugar content decreased by 24.8% at most and reducing sugar content by 34.2% at most. L. plantarum produced the largest amount of acid at fermentation for 48h, while S. thermophilus produced the weakest acid. Protein in beverage was used by Lactobacillus as nitrogen source, and the total protein content decreased by up to 58.6% after fermentation for 48 h. Lactic acid fermentation had little effect on rutin, but it caused a small amount of decomposition of quercetin and kaempferol 3-rutinoside.