In this study, a strain of lactic acid bacteria (LAB) L-19 with high phytase activity selected from spontaneous fermentation black bean substrate was used as starter to prepare black bean sourdough. The fermentation process of black bean sourdough was optimized by response surface design. The growth of LAB and acidity of the sourdough were investigated in the work, and the molecular weight distribution of peptides and the degradation ratio of anti-nutritional factors (ANF) were analyzed during sourdough fermentation. Meanwhile, the baking characteristics of black bean sourdough bread were evaluated. The results showed that LAB L-19 with phytase-producing capacity was identified as Pediococcus acidilactici, and its extracellular and intracellular phytase activity were 1.36 U/mL and 0.30 U/mL, respectively. The optimal fermentation conditions were determined by response surface analysis as followed: DY value 300, fermentation temperature 37 ℃, inoculation quantity 8%. The LAB L-19 grew well in black bean sourdough and showed moderate acidizing ability. Various anti-nutritional factors were effectively degraded in black bean sourdough, the degradation ratio of phytic acid was as high as 62.70%. In addition, a variety of peptide were released due to proteolysis of black bean, of which small molecule peptides accounted for 51.47%. Compared with the control, the overall acceptability of L-19 black bean sourdough bread was also higher. Therefore, the nutritional and sensory quality of product were improved by the LAB L-19 fermentation, and showed a potential application in black bean sourdough bread.