Bifidobacterium suffers from poor timeliness and poor flavor in fermented milk applications due to its own physiological properties. Lactococcus lactis subsp. lactis BL19 was compounded with four strains of Bifidobacterium animalis subsp. lactis for the preparation of fermented milk， and single-strain fermentation was used as a control. The pH value， titratable acidity， viable count， viscosity， water holding capacity， texture， electronic nose， electronic tongue and sensory evaluation of fermented milk in each group during fermentation and storage were measured to comprehensively evaluate the improvement effect of BL19 on the quality of Bifidobacterium animalis subsp. lactis fermented milk. The results showed that BL19 could shorten the fermentation time of Bifidobacterium animalis subsp. lactis fermented milk to 8 h compared with single-strain fermentation and and enable the viable count of Bifidobacterium animalis subsp. lactis to increase rapidly by more than 4 times in a short period. During the storage period， BL19 could reduce the post - acidification degree of Bifidobacterium animalis subsp. lactis fermented milk， maintaining the pH value above 4.33， increase the water - holding capacity to over 60%， keep the viscosity below 2 000 cP， and improve the texture of the fermented milk simultaneously. Moreover， the addition of BL19 enriched the volatile flavor substances in the fermented milk of Bifidobacterium animalis subsp. lactis， and improved the taste and odor of the fermented milk during the storage period. Conclusion: Lactococcus lactis subsp. lactis BL19 had a certain improvement effect on the quality of fermented milk of Bifidobacterium animalis subsp. lactis， which was intended to provide data reference for the application and promotion of probiotic fermented milk in the industrialization process.