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Black soybean meal was used as raw material to prepare lactic acid beverage with antioxidant activity through lactic acid bacteria fermentation. Single factor and response surface methodology were used to optimize the fermentation process of lactic acid bacteria. The effects of the solid-liquid ratio, inoculation quantity, fermentation temperature, and fermentation time on the fermentation process were investigated with DPPH radical scavenging ratio as an index. The DPPH radical scavenging experiment, OH radical scavenging experiment, ABTS radical scavenging experiment, and lipid peroxidation inhibition experiment were tested to assess the antioxidant effect of fermented products. The results showed that Streptococcus thermophilus was the best fermentation strain, and the optimum fermentation processes were solid-liquid ratio 1:5 g/mL, inoculation quantity 5%, fermentation temperature 37.6 ℃, and fermentation time 36 h, respectively. Under the optimal fermentation conditions, the DPPH radical scavenging ratio was 71.56%. The semi-inhibitory concentrations of DPPH, OH and ABTS free radicals in the fermentation products of black soybean meal were 2.43, 1.30 and 0.37 mg/mL, respectively, and the lipid peroxidation was effectively inhibited, indicating that the fermentation products had good antioxidant activity in vitro. The sensory evaluation and suspension stability of beverage were 90.21 and 96.8%, respectively. This study provides a new idea for the development of functional foods with black soybean meal as raw material, and also provides a reference for the further development of agricultural by-products.