Soybean peptides (SOPs) are functional ingredients with good health benefits. The health benefits presented are highly dependent on the peptide structures. SOPs were prepared from soybean protein isolate by hydrolysis. Ultraviolet full wavelength scanning method and circular dichroism spectrophotometry were used to analyze whether the structure of SOPs was affected by pepsin， trypsin and the sequential treatment of pepsin and trypsin. ABTS free radical scavenging ability， DPPH free radical scavenging ability， oxygen radical absorbance capacity (ORAC) and ferric ion reducing antioxidant power(FRAP) of SOPs were measured in order to explore the changes of antioxidant capacity of SOPs before and after digestion. The results showed that SOPs were mainly composed of components with molecular weight less than 1 000 u， and the proportion of components less than 1 000 u increased after digestion， and the maximum proportion reached 88.46%. They all had maximum absorption peaks at 275 nm. In the secondary structure, the proportion of random curl in the four groups of SOPs was about 30%， accounting for about 1/3 of the total secondary structure composition, indicating high disorder and loose and open structure of SOPs. The ABTS free radical scavenging ability and iron reducing ability of SOPs were stable. After trypsin digestion， DPPH radical scavenging rate decreased and oxygen radical absorption capacity increased significantly (P < 0.01).