Degradation of grassland causes changes in internal properties of soil, such as the structure and characteristic of humic acid. Humic acids were extracted from a steppe soil under different degeneration stages. Elemental analysis and 13C nuclear magnetic resonance spectroscopy were used to study the structural changes of soil humic acid in the steppe soil. Structural changes in HA was investigated with Factor Analysis. The results showed that the basic carbon frameworks of HA were similar under different degeneration stages. During the process of degeneration, the content of aromatic carbon, and carbohydrates in soil HA decreased. In addition, the oxidation of HA was increased while the hydrophobicity was declining. During the recovery process, the content of aromatic carbon, and carbohydrates in soil HA increased while the hydrophobicity was declined. The aromaticity and polymerization of HA in S. bungeana area, S. bungeana+A. Sphaerocephala area was higher with lower oxidation; the acidity of HA in fenced area was higher, but the aromaticity and polymerization were lower. The results verified that vegetation recovery imposed an important effect on humic acid structure; besides, aromatic groups and aliphatic groups played an important role in the formation of stable humic acid structure.