This paper summarized professor AI Rudi's experience in treating erythema nodosum by dispelling dampness and dredging collaterals. It is concluded that dampness obstruction and collateral stasis are the core pathogenesis of erythema nodosum. Among them， the long-term accumulation of dampness is the basis， while dampness pathogen flowing through channels and collaterals is the initial factor. Blood stasis obstructing the vessels is the key link in the pathogenesis， and eventually dampness and blood stasis will lead to erythema， nodules， pain and other symptoms. Treatment principle should be dispelling dampness and dredging collaterals， and it is advised to reinforce healthy

qi

and dispel pathogen， and combine the internal treatment with the external treatment. When dispelling dampness， it is also critical to dissolve stasis， and when dredging collaterals， dissipating masses is necessary. For the acute stage， the syndrome of dampness and heat stasis obstruction is commonly seen and mainly treated by clearing heat and draining dampness， promoting blood circulation and dredging collaterals， with orally administered

Modified

Simiao Powder （

加味四妙散） and externally applied

Proven Formula Jinhuang Powder （

验方金黄散）. In the chronic phase， the syndrome of cold and dampness obstructing the collaterals is commonly seen and mainly treated with the method of fortifying the spleen and removing dampness， warming the meridian and dredging the collaterals， with orally taken

Ai's Sijunzi Decoction （

艾氏四君子汤） and

Danggui Sini Decoction

（当归四逆汤） and externally applied

Chonghe Powder （

冲和散）. Integrated internal and external treatment makes a good effect.