Objective:To discuss the clinical significance of diagnosing and treating synovial lipomatosis of knee joint with high-frequency ultrasonography. Methods:50 cases with synovial lipomatosis of knee joint were diagnosed by high frequency ultrasonography and the results were compared with the diagnosis of MRI, and the arthroscopic probe and living tissue pathological examination were done. Results:The ultrasonogram of synovial lipomatosis of knee joint showed that synovial membrane became thick and ultrasonic echo was enhanced and finger or other shapes they assumed floated in the articular cavity which can be transformed with pressure. In addition, CDFI showed no blood flow signal, which provided reliable and simple inspection method for differential diagnosis. It can ensure the gathering position of synovial villi to provide effective guidance for using miniinvasive surgery to treat synovial lipomatosis with arthroscopy. Conclusion:High frequency ultrasonography has a significant clinical application value in diagnosing and treating synovial lipomatosis of knee joint and it should be widely developed.