Medicago archiducisnicolai was endemic to China, distributed in the eastern margin of the QinghaiTibet Plateau, and has developed spreading rhizome. In order to explore the relationship between the abnormal development of M. archiducisnicolai rhizome and plateau climate adaptation, we anatomized the primary and secondary structure of the plant rhizomes by paraffin section. The results showed that: (1) compared with the primary structure, the secondary structure of M. archiducisnicolai rhizome was unbalanced, only a few vascular bundles developed normally, with developed xylem. (2) The secondary growth of rhizome produced two kinds of periderm: inner periderm and outer periderm. The outer periderm was formed by endodermis cells near phloem, and the inner periderm was formed by medulla cells near xylem. After the formation of inner and outer periderm, they replaced the epidermis and the main parenchyma in primary structure, formed a complex new protective system. (3) The inward constriction of the outer periderm or outward extension of the inner periderm could cause the split of the rhizome, but the two types of splits had not been observed at the same time. It was concluded that the formation of inner and outer periderm and abnormal split of the rhizome of M. archiducisnicolai could enhance the resistance to drought and cold stress, which was the adaptive strategy of M. archiducisnicolai to the cold and drought environment of QinghaiTibet Plateau.