The clinical experience of Professor Chu Lixi in treating knee osteoarthritis （KOA） is introduced in this article. It is considered that “arthralgia comes earlier than flaccidity” in the development of KOA， with “arthralgia as the manifestation and flaccidity as the root”. The pathogenesis is characterized by “arthralgia developing into flaccidity， coexistence of arthralgia and flaccidity， and mutual impairment between arthralgia and flaccidity”. Professor Chu emphasizes the importance of combining syndrome differentiation-based treatment and stage differentiation-based treatment， giving considerations to the combined treatment of the whole and the local， the manifestations and the root， as well as arthralgia and flaccidity. Meanwhile， the combined use of oral and external treatment of traditional Chinese medicine is highly valued. Therefore， the principles of “combined internal and external treatment” and “one prescription for three uses” are fully practiced. In view of the internal pathogenesis of “imbalance of sinews and bones”， Professor Chu puts “equal emphasis on the treatment of sinews and bones”， advocating combined use of staged orthopaedic manipulative therapies and functional training to achieve “integrated medical treatment and rehabilitation”. One proven case is presented.