Objective To investigate the regulatory mechanisms of extrusion pretreatment on the protein digestibility of black soybean meal and systematically evaluate its effects on soy sauce quality and antioxidant activity.Methods A mixture of black soybean meal and flour was pretreated using extrusion technology for soy sauce brewing. Extrusion temperature, screw speed, flour addition, and moisture content were selected as the main process parameters to investigate their effects on protein digestibility. Under the optimal extrusion conditions, the raw materials were prepared and further subjected to simulated low-salt solid-state soy sauce fermentation. Amino nitrogen, total nitrogen, reducing sugar, pH, total acid, ammonium salt, soluble salt-free solids, and antioxidant activity (1,1-diphenyl-2-picrylhydrazyl [DPPH] radical-scavenging rate and total phenolic content) were measured to evaluate the effects of extrusion modification on soy sauce quality and antioxidant activity.Results The optimal extrusion parameters were an extrusion temperature of 100.0 ℃, screw speed of 205 r/min, flour addition of 15.5%, and moisture content of 17.8%. Under these conditions, the protein digestibility of the extrudate reached 85.25%, representing a 49.23% increase compared with that of unextruded black soybean meal. Compared with the unextruded group, the amino nitrogen and total nitrogen contents of soy sauce in the extrusion pretreatment group increased by 50.8% and 44.9%, respectively, while the reducing sugar content increased by 36.2%. Meanwhile, antioxidant activity was significantly improved, with the DPPH radical-scavenging rate increasing from 42.6% to 60.3% and the total phenolic content increasing by approximately 42.2%.Conclusion Extrusion pretreatment can significantly enhances protein digestibility and, through the synergistic effects of moderate denaturation and starch gelatinization, improve the enzymatic hydrolysis efficiency and generation of flavor precursors in soy sauce fermentation substrates, while enhancing the antioxidant function of the product.