Abstract: As an important microbial resource in the fields of food, agriculture and medicine, lactic acid bacteria have good development prospects. A long period of production experience has found that some important biochemical reaction process is difficult to complete by one bacterial starter during fermentation, and two or more microbial co-culture, namely mixed culture, are needed. This paper briefly describes the interaction mechanism between different lactic acid bacteria strains in fermented milk and the effect of mixed culture of lactic acid bacteria on the sensory and nutritional characteristics of fermented dairy products. Uncover the interaction mode and mechanism among lactic acid bacteria flora in fermented milk is conducive to improving substrate conversion rate and process performance of product, which provides a theoretical reference for lactic acid bacteria co-culture in yield regulation, product functionalization and resource utilization.