Objective： Extracellular polysaccharides（EPS）， as important secondary metabolites of lactic acid bacteria （LAB） play an important role in the production of fermented dairy products. Therefore， it is necessary to analyze the molecular mechanism of EPS production by lactic acid bacteria by bioinformatics in order to provide theoretical basis for the development and utilization of EPS. Methods：In this experiment， the second generation sequencing technology （Illumina Hiseq 4000） and Real-time fluorescent quantitative PCR（RT-qPCR） were used to sequence the genome of a strain of Streptococcus thermophilus IMAU20756 with high production of EPS from Mongolian yoghurt and quantitative analysis of eps gene expression at different time points. Results： The total genome length of the strain was 1 838 440 bp and GC contained 38.8%. In addition， it encoded 2 120 genes， including 1 962 functional genes， 36 tRNA， 515 pseudogenes， 1 tmRNA and 2 repetitive units. Among them， there are 12 genes related to EPS production. EpsA and epsB are regulatory genes， epsC and epsD determine the chain length of polysaccharides， eps1E， eps2E， epsG， epsF， epsH， epsI and epsJ are genes that encode glycosyltransferase， and epsK regulates the polymerization and output of polysaccharides. Conclusion： All the genes related to EPS biosynthesis could be expressed during fermentation， especially the gene expression of glycosyltransferase was the highest at 6 h of fermentation.