Abstract: To analyze the physicochemical parameters and bacteria community structure in the Koumiss 's fermentation process( 0 ~ 96 h). The main findings were introduced in following part. During the fermentation process,the p H value of Koumiss was declined at high speed in early period and then the decent speed was slowed down and finally reached to the minimum value( p H = 3.54). The total contents of protein and fats were fluctuant changed,and achieved to the maximum values at 72 h. The content of lactose was decreased,while the lactic acid was increased in the process of fermentation. The contents of glucose,galactose,acetic acid,and propionic acid were at low level during fermentation.The results of bacterial community structure analysis showed that there were abundant bacterial diversity and their dynamic community structures changed obviously in the Koumiss fermentation process. Lactobacillus was the dominant bacterial genus. Its content showed a rising trend during 12 h to 24 h,while decling at 24 h to 48 h.The result showed that there were differences in nutritional value of Koumiss at different fermentation period.