Objective To observe the application value of musculoskeletal ultrasound (MSUS) in the efficacy of knee osteoarthritis (KOA) joint fluid by needleknife treatment. Methods 60 patients with KOA admitted to the hospital from February 2017 to February 2018 were selected and treated with needle-knife for 5 weeks, and they were given MSUS before and after treatment. The joint effusion thickness, synovial thickness, grades of synovial blood flow signal and cartilage stages of knee joint were observed, and pain visual analogue scale (VAS) score and Lequesne index score were recorded. Results Compared with before treatment, the joint effusion thickness and synovial thickness were significantly reduced after treatment (P＜0.05), and the grades of synovial blood flow signal were significantly improved (P＜0.05), showing time dependence (P＜0.05). There were no significant changes in cartilage stages of knee joint before and after treatment P＞0.05). Compared with before treatment, the knee pain VAS score and Lequesne score were significantly decreased after treatment (P＜0.05), showing time dependence (P＜0.05). Spearson correlation analysis showed that the ultrasound indexes of joint effusion thickness, synovial thickness and grades of blood flow signal before and after treatment were positively correlated with VAS score and Lequesne score (P＜0.05). Conclusion MSUS examination shows that needleknife treatment can improve joint effusion, synovial thickness and synovial blood flow signal in patients with KOA, which is of great significance for the evaluation of efficacy.