Abstract: Complex microbial metabolism is key to the unique flavor formation of Chinese fermented mandarin fish (mackerel). In this study, gas chromatography-ion mobility spectrometry (GC-IMS) was used to analyze the formation of volatile flavor compounds in fermented mackerel and high-throughput sequencing of 16S rRNA technology was used to analyze the succession of bacterial populations during mackerel fermentation, revealing the relationship between functional microorganisms and volatile properties in mackerel fermentation. Results showed that there were 51 volatile flavor components in mackerel fermentation process, mainly including esters, alcohols, acids, ketones, aldehydes, furans and others. The main dominant bacterial genera included Lactobacillus, Staphylococcus, Macrococcus, etc. The correlation analysis results showed that Lactobacillus was the main factor that led to the high contents of ketones and alcohols. The Staphylococcus played an important role in the production of esters in mackerel, and negatively correlated with ketones. Although the relative abundance of Weissella, Acinetobacter, Methylophilus and other microorganisms was not high, they were also significantly correlated with the formation of volatile flavors (P<0.05). This study would provide the bacterial genera for improving the quality mackerel and controlling the fermentation process.