Abstract: To screen yeast strains which are excellent symbiosis with Lactobacillus delbrueckii in yoghourt fermentation in this paper,the yoghourts were fermented with Lactobacillus delbrueckii mixed with 27 yeast strains isolated from the traditional dairy products collected from Xinjiang, Tibet, Qinghai and other regions. Then, these yoghourts were compared with the yoghurt fermented only with Lactobacillus delbrueckii on the milk curd time,sensory evaluation,texture,titration acidity,viscosity,the content of diacetyl and acetaldehyde to screen symbiotic yeast excellent performance in yoghourt fermentation. The excellent symbiotic yeast strains were identified based on 26S D1/D2 region and ITS1 sequence.The results showed that 27 strains of yeast were not significantly different on the milk curd time.But the yoghourts co-fermented with 9 yeast strains had scores at more than 80 in sensory evaluation.Among them,the yoghourts co-fermented with "XS1" had excellent performance in texture, titration acidity at 4° T, viscosity at 100%, the content of diacetyl at 12.65 μg/mL and acetaldehyde at 7.19%. The strain "XS1" was classified as Kluyveromyces marxianus with molecular biology methods.The strain "XS1" could provide reference for the development of new yoghurt.