ObjectiveThis study aims to investigate the inhibitory effect of Wutoutang on pannus formation in adjuvant-induced arthritis （AIA） rats with wind-cold-dampness Bi syndrome and its potential mechanism. MethodA total of 40 male SD specific pathogen-free （SPF） rats were selected and divided into blank group， wind-cold-dampness Bi syndrome group ［Complete Freund's Adjuvant （CFA）， 200 μg］， Wutoutang group （15 g·kg^-1·d^-1）， and indometacin group （10 mg·kg^-1） according to random number table method. Except for the blank group， the other groups were given wind-cold-dampness stimulation before the CFA injection. After the rats were administered for 30 days， the basic conditions， onset time， arthritis index score， and foot swelling volume of AIA rats with wind-cold-dampness Bi syndrome were observed. Finally， peripheral arterial blood， ankle joint， and synovial tissue were taken. Enzyme-linked immunosorbent assay （ELISA） was used to detect serum hypoxia-inducible factor-1α （HIF-1α）， vascular endothelial growth factor A （VEGFA） protein content， and rheumatism， including anti-O （ASO）， C-reactive protein （CRP）， and rheumatoid factor （RF）. Hematoxylin-eosin （HE） staining revealed the changes in joint histomorphology. Immunohistochemistry was used to detect the expression of HIF-1α and VEGFA， two important proteins in the ankle pathway. Quantitative real-time polymerase chain reaction （Real-time PCR） was used to reveal mRNA levels of HIF-1α， VEGFA， angiopoietin-1 （Ang-1）， and angiopoietin-2 （Ang-2） in rat synovial tissue. ResultThe foot swelling volume and arthritis score of AIA rats with wind-cold-dampness Bi syndrome were substantially higher （P<0.01） compared with the blank group. Serum CRP， RF， and ASO levels were considerably elevated （P<0.01）. HE staining showed obvious hyperplasia of ankle synovium and synovial inflammation， angiogenesis and pannus formation， and aggravated bone destruction， indicating successful modeling. After the intervention of Wutoutang， the onset time was delayed （P<0.01）. Foot swelling volume and arthritis score were decreased （P<0.01）. Serum CRP， RF， and ASO levels were significantly decreased （P<0.01）. The inflammatory hyperplasia of synovial tissue， angiogenesis and pannus formation， and bone destruction were alleviated. The mRNA levels of HIF-1α， VEGFA， Ang-1， and Ang-2 in the synovial membrane were significantly decreased （P<0.05， P<0.01）. The expressions of HIF-1α and VEGFA in serum and ankle joints were decreased （P<0.01）. In the indomethacin group， the onset time of the disease was delayed （P<0.01）. Foot swelling volume and arthritis score were decreased （P<0.01）. Serum CRP， RF， and ASO levels were significantly decreased （P<0.01）. HIF-1α/VEGFA/Ang signaling pathway was activated， and pathological tissue injury was improved. ConclusionWutoutang can delay the onset time of AIA rats with wind-cold-dampness Bi syndrome， reduce foot swelling volume， arthritis score， rheumatic activity， and improve joint histopathology. It can inhibit pannus formation， and its mechanism may be related to down-regulating the expression of the HIF-1α/VEGFA/Ang pathway.