Abstract: Five strains from yak milk in Tibetan Pastoral Areas with better fermentation performance were mixed,and their best fermentation combination was studied. The results showed that Thermophilic streptococcus Q4 and lactobacillus Bulgaricus subspecies G4 were the best combination,and its performance was superior to that of the single bacterium. The antipost-acidification capability of the yogurt which was fermented by Q4-G4 increased,and both the number of living bacterium(greater than 109cfu/m L) and viscosity(7.4 ⁸.61 Pa·s)were higher than that of the single strain,and the aroma-producing capacity improved. All of these kept the yogurt flavor better. Additionly extracellular polysaccharide content of the yogurt(129.28 mg/m L) was significantly higher than that of single strain. There was not significant difference both Q4-G4 and the commercial starter cultures YO-MIX300 in fermentation performance. Therefore,Q4-G4 could be used mixed starter culture and applied into yogurt industralization production.