Abstract: Putting mare's milk beer as investigation object,the mare's milk beer fermentation control parameters had been conformed by the control of single factor experiment for determine the four factors,judgment step length,Simplex algorithm.The results showed that the best fermentation parameters had been selected as the inoculation amount 8%( Bacillus casei ∶ Kluy-veromyces marxianus = 1∶ 1),set 35 ℃ as fermentation temperature,set fermentation time as 48 h,set 9% and 30% as sucrose content and malt juice.Under this condition,p H was selected as 3.30 ± 0.02,degree of alcohol was selected as 5.4% ± 0.2%vol,sensory score was selected as 79 ± 1.4.All indexes above all inculds sensory,physical and chemical,sanitary were recognized by national standard named “GB19302-2010 fermented milk”.Foundation of theory and practice was provided by the study of control of the mare's milk beer fermentation for the diversity of mare's milk and its products in Xingjiang.