In this experiment, 10 strains of Streptococcus thermophilus strain from Shenzhou-11 return spacecraft was isolated and purified. The growth curve, titration acidity, viscosity and extracellular polysaccharide content of wild strain G2 and test strains were measured, and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) tests were performed. The results showed that OD600 value of two strains B2-1 and B2-4 (2.073±0.15, 2.06±0.11), titration acidity (106±0.23) °T, (98.5±0.25)°T, viscosity (3.27±0.04) Pa·s, (2.94±0.01)Pa·s, and Extracellular polysaccharides (409.35±1.38) mg/L, (398.80±5.38) mg/L were all higher or significantly higher than those of wild strain G2 with OD600 of (2.051±0.11 ), Titration acidity of (92±0.16) °T, viscosity of (2.66±0.07 )Pa·s and extracellular polysaccharide content of (385.11±3.074) mg/L. Finally, two strains of Streptococcus thermophilus with excellent characters of B2-1 and B2-4 were obtained. Therefore, space mutation breeding may change the Streptococcus thermophilus fermentation performance.