In order to study the interaction between the dominant bacterial community of Koumiss and the relationship between the bacterial community and characteristic flavor， this experiment conducted mono- or co-cultures fermentation of 4 strains of lactic acid bacteria (LAB) and 2 strains of yeast isolated from traditional Koumiss， and measured the acidity， pH， changes in the amount of LAB and yeast in 14 groups of fermentation group. HS-SPME-GC-MS was used to study the differences of volatile flavor compounds in different fermentation groups. Lotka-Volterra model and partial least square regression (PLSR) were used to analyze the interaction coefficient between LAB and yeast and the correlation between dominant bacteria and the formation of characteristic flavor compounds in Koumiss. Lactobacillus casei (L. casei) had the fastest acid production rate among LAB， with pH value of 3.89 in the late stage of fermentation. For yeast， pH value of Kluyveromyces marxianus (K. marxianus) dropped to 4.16. The acid production of co-culture fermentation group was better than that of mono-culture fermentation group. The fermentation of LAB and Kazachstania unispora (K. unispora) can promote the growth of K. unispora. After 72 h of mixed fermentation with K. unispora， the bacterial colonies of Lactobacillus plantarum (L. plantarum) and Lactobacillus paracasei (L. paracasei) reached 1.91 × 106 CFU/mL and 1.66 × 106 CFU/mL， respectively. Also， it promoted the production of caprylic acid and n-decanoic acid. While the mixed fermentation of LAB and K. marxianus can form competitive inhibition. Also， the production of ethyl octanoate and ethyl caprate was inhibited in the co-fermentation system. The inhibitory effect on L. casei and Lactobacillus paracasei (L. paracasei)， which produce acid rate faster， was stronger than the L. helveticus and L. plantaru).