Abstract:Soybean billet was fermented by lactic acid bacteria producing acid.Pre-fermentation was carried out by inoculating Actinomucor elegans without salting.And lactic acid bacteria LB01 and Clostridium butyricum BP01 were added to the soup in the late fermentation.The key flavor substances and some functions were studied.The results showed that the relative content of indole and other amines could be decreased by adding probiotics and the edible safety of grey sufu could be improved in some extent.The γ-aminobutyric acid（GABA）content of samples increased through low-salt fermentation，and the GABA contents of low-salt sample 1 and 2 were 188.92 mg/100 g dry weight and 223.95 mg/100 g dry weight，respectively，which were 1.33 times and 1.57 times of the control sample.The content of butyric acid increased by adding Clostridium butyricum to fermented soup.There was no significant difference in the content of butyric acid between the control and low-salt samples 1，but the content of butyric acid in low-salt samples 2 was 39.46%higher than that of the control.Low-salt sufu had acetylcholinesterase inhibitory activity，but there was no significant difference between the low-salt sufu and the control，but the inhibition activity of angiotensin converting enzyme（ACE）and the content of peptides in low-salt sufu were significantly higher than those of the control（P＜0.05）. Key words：low-salt sufu；lactic acid bacteria；Clostridium butyricum；functional characteristics；key volatile flavor substances