Objective:To observe and objectively evaluate the clinical efficacy of milli-fire needle in the treatment of knee osteoarthritis of cold-dampness blockage type complicated with synovitis by musculoskeletal ultrasound. Methods60 patients with knee osteoarthritis of cold-dampness blockage type complicated with synovitis were assigned into the treatment group and the control group according to the random number table, 30 patients in each group. Patients in the treatment group were treated with milli-fire needle plus TDP irradiation, while those in the control group received simply acupuncture plus TDP irradiation. Patients in both groups were treated for 2 weeks. Synovial thickness and joint effusion depth in the knee joint were observed based on musculoskeletal ultrasound and the changes in VAS pain score, WOMAC score and knee joint circumference were compared.  Results:① There were statistically significant differences in synovial thickness and joint effusion depth in both groups before and after treatment (P<0.05). After treatment, there were statistically significant differences in synovial thickness and joint effusion depth between the groups, and improvement in the treatment group was significantly superior to that in the control group (P<0.05). ② There were statistically significant differences in VAS pain score and WOMAC score in both groups before and after treatment (P<0.05). After treatment, there were statistically significant differences in VAS pain score and WOMAC score between the groups, and the scores were significantly lower in the treatment group than in the control group (P<0.05). ③ There was statistically significant difference in knee joint circumference in both groups before and after treatment (P<0.05). After treatment, there was statistically significant difference in knee joint circumference between the groups, and the circumference was significantly smaller in the treatment group than in the control group (P<0.05).  Conclusion:Compared with simply acupuncture, milli-fire needle shows a better clinical efficacy in the treatment of knee osteoarthritis of cold-dampness blockage type complicated by synovitis. It effectively relieves the pain of patients, reduces knee joint swelling, improves synovial lesions, and reduces joint effusion.