Abstract: Electronic nose, gas chromatography-mass spectrometry(GC-MS), amino acid analyer were employed to investigate the flavor substances and amino acids of thirteen kinds of natural plain fermented soy sauce. Meanwhile, sensory evaluation was combined to analysis the components differences of different products.The results showed that raw materials and fermentation technology were the main factors leading to different flavor and quality of soy sauce. According to the analysis of physical and chemical indexes, the change of ethanol and total sugar content in different products were the most obvious. Ethanol, nitrogen oxides and inorganic sulfides were the main material bases of flavor differences in soy sauce. The free amino acid composition of soy sauce not only had a significant impact on the flavor characteristics of soy sauce, but also directly or indirectly affect the flavor characteristics of soy sauce, such as umami, salty, sweet and sour, together with sugar, acid and total nitrogen. According to the comprehensive analysis, when amino acid nitrogen was greater than 1.00 g/100 mL, total nitrogen ≥1.80 g/100 mL, the sugar content was higher than 6.0 g/100 mL, the sugar/acid ratio was 3.40~5.80, the free amino acid content was higher than 60 mg/mL, soy sauce flavor quality would be pleasant. The results of this study were helpful to supplement and improve the flavor fingerprint of soy sauce, guide the establishment of quality evaluation standards of soy sauce, and could also be used to evaluate the production process and technical conditions and guide the actual production.