Abstract: To study the changes of flavor substances in the high-salt dilute fermentation process of soy sauce brewed by adding red koji complex, the volatilization in the dilute mash was analyzed by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). For analysis of sexual flavor substances, it was determined that the best conditions for solid-phase microextraction of dilute mash were: 75 μm CAR/PDMS extraction head, 2.5 g sodium chloride, extraction temperature 50 ℃, extraction time 30 min. Under these conditions, the quantity and proportion of volatile substances in different soy sauces were analyzed, and it was found that meniscus soy sauce had a higher proportion and abundance of esters than other soy sauces, and it was fermented for thin mash10, 30, 50, 70, 80, 120, 160 d samples detected alcohols (14 types), acids (7 types), ketones (9 types), esters (15 types), phenols (6 types), Aldehydes (3 types), pyrazines (3 types), pyrroles (1 type), alkenes (1 type), furans (2 types) and others (4 types), a total of 65 substances. By comparison, it was found that the content and types of esters in the volatile substances of monascus soy sauce were the most abundant, and they were the main substances that constitute the flavor of monascus soy sauce. Through heat map analysis, it was found that the content of aldehydes ketones, pyrazines, and pyrrole substances was produced from 0~120 days of thin mash fermentation. Alcohol substances increased significantly during the whole fermentation period, and 80~180 days of thin mash fermentation was the period of significant increase of phenols, acids, and esters. The increase of ester flavoring substances indicated that the addition of red yeast significantly enhanced the flavor of ester and improved the flavor of soy sauce.