Abstract: Antitumor drug-related oral mucositis (ADOM) is one of the most common oral complications in cancer patients receiving chemotherapeutic agents, targeted drugs, immune checkpoint inhibitors (ICIs), and other medications. Professor Huo Jiege, a renowned Traditional Chinese Medicine (TCM) practitioner in Jiangsu Province, based on the pathogenesis of ADOM, proposed the theory of “deficiency-stagnation-collateral damage”. He posits that the occurrence of ADOM is rooted in “deficiency”, manifested as “stagnation”, localized in the “collaterals”, and resulting in “damage”, with the pathological evolution following the pattern of “deficiency-stagnation-collateral damage”. Antitumor drugs (medicinal toxins), as a special form of “attacking pathogenic factors”, first consume the body’s qi, blood, yin, and yang, leading to a deficiency of healthy qi. Subsequently, pathological factors such as qi stagnation, blood stasis, and phlegm-dampness intertwine, forming a local state of congestion. Ultimately, this results in prolonged stasis transforming into heat, causing heat-induced decay and collateral damage. Based on this, a composite treatment method of “supplementing qi, reinforcing the body, replenishing deficiency, consolidating the foundation; promoting qi circulation, activating blood, resolving phlegm, dispersing stagnation; cooling blood, unblocking collaterals, generating tissue, and repairing damage” was formulated. This theory provides an important theoretical basis and clinical reference for the prevention and treatment of ADOM.