Cartilage is an important structure of the knee joint, playing a role in lubricating the joint and cushioning pressure within the joint cavity. Cartilage injury can lead to knee osteoarthritis (KOA), severely affecting patients' quality of life. Current clinical methods used to treat KOA cannot repair damaged cartilage. In recent years, synovial mesenchymal stem cells (SMSCs) have shown unique advantages in repairing cartilage injuries, making it a hot research field for cartilage repair. Therefore, this article provides a comprehensive review of the mechanisms and research progress of SMSCs in repairing cartilage injuries, with the aim of promoting the clinical translation of SMSCs in cartilage repair.