The key flavor compounds of fermented milk produced by six strains of S. thermophiles isolated from different regions were analyzed by solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) technology, combined with aroma threshold and relative odor activity value (ROAV). The results showed that the total of 63 volatile compounds were finally detected in these fermented milk, including aldehydes, ketones, acids, esters, alcohols, aromatics, and hydrocarbon compounds. Among them, 12 kinds of volatile compounds, such as diacetyl, acetoin, acetaldehyde, and 2-nonanone had higher ROAV (ROAV≥1), which contributed greatly to the overall flavor of fermented milk. Principal component analysis and comparative analysis of similarity demonstrated that there was a high similarity among the flavor compounds of S. thermophilus fermented milk from the same area while that from different regions was lower. The results indicated that the pressure of growth environment can exert an influence on the aroma-producing characteristics of the fermented milk of the strain.