Objective: To explore the changes of metabolites and antioxidant activity of soybean based plant fermentation broth during fermentation. Methods: The experiment was conducted to prepare the compound fermentation liquid from kidney beans and soybean by fermentation of yeast, Lactobacillus and other probiotics, The pH value, total acid, reducing sugar, soluble solids, total phenol, flavone content and antioxidant activity in the fermentation process were analyzed. Results: The pH value of fermentation broth decreased with the extension of fermentation time and gradually stabilized at about 3.55, the total acid content increased from 0.13 mg/mL to 0.43 mg/mL, and the soluble solid content decreased from 10.01% to 5.73%. The content of reducing sugar decreased at first and then kept fluctuating balance. The total phenol content increased rapidly in the fermentation process, and then stabilized at about 430 mg/mL. The content of flavonoids also increased with the fermentation, and then stabilized at 155.30 μg/mL. The reducing power and ABTS free radical scavenging capacity of fermentation broth showed a continuous growth trend, and reached a stable state in the late stage of fermentation, reaching the maximum value （0.608 and 3.404 mmol/L） at 48 h of fermentation, respectively. Conclusion: There is a certain regularity in the change trend of conventional metabolic components in kidney bean and soybean compound fermentation broth, and the fermentation broth has a certain antioxidant capacity.