Abstract: Two Yoghurt strains were isolated and selected from import yoghurt culture and their fermented characteristics was studied in this paper. 4 strains of Lacticum delbrueckii subsp. Bulgaricus and 4 strains of S. sativarius subsp. thermophilus were isolated from yoghurt culture respectively. The screening of the fine yoghurt strains was comprehensive assessment according to the level of acidproduced flavour and texture of yoghurt. By this method,two fine strains of yoghurt strains were identified,namely L. bulgaricus L9 and S. thermophilus S5. Results showed that the symbiosis of these two strains in milk was perfect,which optimal combination of inocula of strain L9∶S5 was 2∶1（V/V）. The results of this study could provide excellent production strains for direct vat set （DVS）.