This article introduced Professor YEHai's clinical experience in treating knee osteoarthritis（KOA）. KOA is a disease with high incidence and disability rate. Clinically，it is mainly characterized by knee joint swelling，stiffness，poor mobility and functional impairment. Severe cases may result in joint deformities，and as the disease progresses and worsens，it can lead to muscle atrophy and even disability. KOA belongs to the category of “knee Bi syndrome” and “Hexifeng” in traditional Chinese medicine. Its cause is mostly due to old age，insufficient Qi and blood，and dysfunction of Zang-organs，leading to endogenous cold and dampness or external wind cold and dampness. If the circulation of Qi and blood is not smooth，blocking the meridians and causing pain，and then resulting in this disease. The persisting condition，recurrent attacks，prolonged illness entering the meridians，and Qi and blood failing to nourish the muscles and bones，could make the muscles，bones and tendons lack of nourishment，and the marrow will lose nourishment. Professor YE Hai believes that the key pathogenesis and pathological characteristics of KOA in the elderly are “congenital deficiency，acquired disorder，liver-Qi stagnation，cold-dampness phlegm and blood stasis”，which affect each other. Clinical patients often develop blood stasis due to deficiency，phlegm due to deficiency，colddampness and blood stasis and accumulation of phlegm-blood stasis. Professor YE Hai is skilled in using the treatment principles of tonifying spleen and kidney，soothing liver and regulating Qi，dispelling cold and dampness，and resolving phlegm and blood stasis to treat this disease，which can achieve good clinical results.