Streptococcus （St.） thermophilus is one of the most commonly used starters in fermented milk production. In the present study， St. thermophilus IMAU80285 isolated from the traditional fermented dairy product qula with specific flavor properties was selected and detected for the flavor substances produced during the production and storage of fermented milk， by gas chromatography-mass spectrometry methods. Principal component analysis and similarity analysis was then used to systematically analyze the flavor components. The results showed that the total of 84 volatile compounds were finally detected in fermented milk during fermentation and storage， including aldehydes （13 species）， ketones（12 species）， acids （11 species）， esters （9 species）， alcohols （22 species）， hydrocarbon compounds （14 species） and nitro-gen-containing compounds （3 species）. Principal component analysis revealed that the apparent distinction in the flavor substance （OAV ≥ 0.1） between the initial stage of fermentation （4， 6 h of fermentation） and the completion of fermentation and whole storage period （after ripening， 1， 2， 3， 7， 14 d）. At the beginning of fermentation （4， 6 h of fermentation） and at the completion of fermentation， there were positive correlations with 17 kinds of flavor substances with OAV ≥ 0.1， such as acetoin， heptaldehyde， 1-nonanol and ethyl hexanoate； while positive correlations were observed with 7 kinds of flavors with OAV ≥ 0.1， such as 2，3-butanedione， 3-methyl-1-butanol and ethyl butyrate during storage （after ripening， 1， 2， 3， 7， 14 d）. The results of overlapping chromatogram and similarity analysis showed that the flavor substances in fermented milk changed significantly during the production and storage of fermented milk. It is obviously noting that significant difference in composition of flavor substances with the increase of storage time.