Objective: To investigate the effects of small needle knife technique guided by musculoskeletal ultrasound on the pain degree, EMG signal and lumbar range of motion in patients with lumbodorsal myofascial pain syndrome (MPS). Methods: Seventy-eight patients with lumbodorsal MPS in our hospital from June 2020 to July 2021 were selected and divided into two groups (study group and control group, with 39 cases in each group) according to random number table. The control group was treated with traditional acupotomy, and the study group was treated with small needle knife technique guided by musculoskeletal ultrasound. The degree of pain, EMG signal and lumbar range of motion 4 weeks after treatment were compared between the two groups. Results: After treatment, the VAS scores of the two groups were lower than before treatment (P < 0.05), and the VAS score of the study group was lower than that of the control group (P < 0.05). After treatment, the median frequency of lumbar core muscle during isometric contraction test in the study group was higher than that before treatment (P < 0.05), and higher than that in the control group (P < 0.05). After treatment, the lumbar range of motion in the study group was larger than that before treatment (P < 0.05), and larger than that in the control group (P < 0.05). Conclusion: The small needle knife technique guided by musculoskeletal ultrasound can significantly reduce the pain degree, improve the EMG signal and lumbar range of motion in patients with lumbodorsal MPS.