Cajanus cajan (L.) Millsp. leaves (CCML), a well-known traditional Chinese medicine, is widely recognized for its protective effects against osteoporosis and osteonecrosis. CCML has been extensively used in the treatment of femoral head necrosis and osteoarthritic infections. This review provides a comprehensive overview of the current research on CCML, focusing on its medicinal phytochemistry, pharmacological activities, molecular mechanisms, safety profile, and clinical applications. An extensive literature review was conducted using online databases, including Web of Science, Google Scholar, Scopus, ScienceDirect and PubMed, as well as pre-electronic literature sources obtained from university libraries. A diverse collection of bioactive substances was identified in CCML, including flavonoids, flavonoid glycosides, stilbenes, flavonostilbenes, steroids, and triterpenoids. Pharmacological studies have demonstrated that extracts and isolated components from CCML exhibit various bioactivities with different mechanisms. Notably, CCML has been developed into an in-hospital preparation for treating femoral head necrosis and osteoarthritic infections over four decades. In conclusion, this review summarizes the chemical compositions, molecular mechanisms, pharmacological activities, and clinical applications of CCML, providing a valuable reference for further research and supporting its potential for advanced development and broader utilization.