A Lactobacillus plantarum (strain CAU: 228) with high free soybean isoflavone was screened from Maotai Qu starter to make soybean sourdough and breads. The changes of the content of 4 kinds of isoflavone monomers, total phenols during the fermentation of sourdough and the molecular weight distribution of soybean peptide before and after fermentation were analyzed. The antioxidant activity and nutritional characteristics of wheat bread, soybean bread and soybean sourdough bread were compared. The results showed that the total isoflavone aglycone content of LAB soybean sourdough was 9.87 times higher than that of unfermented sample. The total phenol content increased from 3.83 mg GAE/g to 5.29 mg GAE/g. The content of antioxidant peptides increased significantly. The total isoflavone aglycone content in soybean sourdough bread reached 6.39 mg/100g, which was 2.93 times of that of soybean bread. The total free amino acid content of soybean sourdough bread was 2.02 and 2.84 times higher than that of soybean bread and wheat bread. The antioxidant capacity of soybean dough bread DPPH and ABTS was also significantly higher. Therefore, this LAB strain has a high potential for application in soybean sourdough bread.