Abstract： Objective： To observe the effect of application of high- frequency ultrasound in micro acupotomy treating lumbodorsal myofascial pain syndrome(MPS)．Methods：A total of 74 cases of patients with lumbodorsal MPS were selected and divided into the observation group and the control group according to the random number table method，37 cases in each group. The control group was given routine micro acupotomy， and the observation group was additionally given micro acupotomy guided by high-frequency ultrasound．In the two groups，the treatment was carried out once every three days， for a total of three times. The clinical effect was compared between the two groups. Before and after treatment， the ultrasonography result as well as scores of Visual Analogue Scale(VAS) and Japanese Orthopaedic Association(JOA) for pain in low back was compared between the two groups. Results： The total effective rate was 94.59% in the observation group，higher than that of 82.97% in the control group(P＜0.05)．After treatment，the elastic scores of myofascial trigger points(MTrPs) in the two groups were decreased when compared with those before treatment(P＜0.05)， and blood flow velocities were increased(P＜0.05)．After treatment，the elastic score of MTrPs in the observation group was lower than that in the control group(P＜0.05)，and blood flow velocity was faster(P＜0.05)．After treatment，scores of VAS in the two groups were decreased when compared with those before treatment(P＜0.05)，and the score in the observation group was lower than that in the control group(P＜0.05)；scores of JOA in the two groups were increased when compared with those before treatment(P＜0.05)，and the score in the observation group was higher than that in the control group(P＜0.05). Conclusion： In the treatment of MPS，micro acupotomy guided by high-frequency ultrasound can enhance clinical effect and the lumbar function，effectively improve elasticity of MTrPs and blood flow velocity，and relieve pain.