Erythema nodosum is a type of panniculitis, often manifests as acute onset, swelling, painful, non-ulcerated red lumps. It is quite common in the extension side of the lower extremities in 20 to 30 years old female.Most patients' onsets of Erythema nodosum are not clear yet. Some of them might be related to certain infectious diseases such as streptococcal infection, TB, certain pancreatic diseases, and some immune deficiencies such as SLE etc. Because erythema nodosum often takes place in the lower extremities, we found similar descriptions in Chinese Medicine archives such as ”san li fa” and ”stagnation of dampness and toxin”. This article discusses the etiology, mechanism and Chinese medicine treatment of erythema nodosum.