Objective:To explore the difference in composition and antioxidant activity of crude extracts of fermented soya beans with different solvent extracts.Methods:70% ethanol was used the extraction solvent, the fermented soya beans powder was extracted by ultrasonic method. After the solvent was evaporated, the crude extract was obtained. The crude extract was dispersed in water and extracted with petroleum ether, dichloromethane, ethyl acetate, and n-butanol in turn to obtain different solvent extracts. The colorimetry was used to determine the content of total flavonoids and total polysaccharides in crude extracts and different solvent extracts, HPLC was used to determine the content of 6 kinds of soybean isoflavones including daidzein. Then their scavenging effects were studied on DPPH free radicals, ABTS free radicals and OH free radicals, and the correlation was analyzed between antioxidant capacity and total flavonoids, total polysaccharides, and 6 kinds of soybean isoflavones.Results:The ethyl acetate extract had the highest total flavonoid content, which was (92.912±1.130) mg/g extract; The n-butanol extract had the highest total polysaccharide content, which was (83.381±0.754) mg/g extract, and the total content of isoflavones in the n-butanol extract was higher than the crude extract and other extracts. The crude extract of fermented soya beans and various solvent extracts showed in vitro antioxidant activity, among which n-butanol extract had the strongest in vitro antioxidant activity. The content of total flavonoids was significantly correlated with the content of 5 soybean isoflavones and antioxidant activity (P＜0.05).Conclusion:The n-butanol extract had a strong scavenging effect on three kinds of free radicals and could be used as a natural antioxidant.