Abstract: In order to solve the problems of long fermentation period and difficult flavor control of traditionally fermented fish sauce, we screened a salt fermenting anaerobic bacterium (Halanaerobium fermentans) YL9-2 related to the flavor formation of traditional fish sauce from the fermentation broth of traditional fish sauce. The results show that YL9-2 could increase the content of amino acid nitrogen and shorten the quality formation time in fish sauce significantly. Meanwhile, its addition improved the food safety of fish sauce significantly, and the mass concentrations of histamine, tyramine, putrescine, cadaverine, tyramine and total biogenic amine decreased by 26.4%, 27.1%, 9.4%, 39.8%, 69.4% and 25.7% at the end of the fermentation. Besides, we applied headspace solid-phase microextraction gas chromatography-mass spectrometry to analyze the volatile flavor compounds in fish sauce. A total of 38 volatile compounds were identified. At the end of the fermentation, the concentrations of isovaleraldehyde, 2-methylbutanal, hexanal, heptanal, n-octanal, n-nonanal, 1-pentene-3-ol, 1-octen-3-ol, 2-nonone and 2-hendecanone respectively increased by 79.7%, 92.5%, 45.3%, 41.8%, 21.2%, 29.4%, 20.4%, 46.6%, 67.7% and 47.2%, which enhanced the malt, grass, cheese, fruit, mushroom, sweet and fatty flavors of fish sauce significantly. The trimethylamine concentration decreased by 61.7% compared with that during natural fermentation, significantly reducing the fishy taste of fish sauce. The results provide important technical supports for the targeted improvement of the quality, flavor and food safety of traditionally fermented fish sauce.