Objective：To investigate the effect of low intensity focused ultrasound（LIFU） on the repair of chronic skeletal muscle in－jury in rats. Methods：An impactor was used to establish a rat model of chronic skeletal muscle injury，and then the rats were divided into ultrasound group and control group. The rats in the ultrasound group were given LIFU once a day for 14 consecutive days，and those in the control group were given sham treatment. Tissue samples of the injured area were collected on days 3，10，and 21 of treatment，and HE staining was used to observe histological changes. Immunohistochemistry was used to measure the expression of Myf-5 and α-actinin；image analysis software was used to measure average optical density（AOD）；real-time quantitative polymerase chain reaction was used to measure the mRNA expression of MyoD. Tissue repair was also evaluated. Results：HE staining showed that necrotic muscle fibers were gradually replaced by newly formed muscle fibers in ordered arrangement in the ultrasound group，while the formation of fibrous tissue，inflammatory cell infiltra－tion，and marked muscle fiber atrophy were seen in the control group. Compared with the control group on days 3，10，and 21 of treatment，the ultrasound group had higher expression of α-actinin（0.270±0.026/0.244±0.011/0.222±0.031 vs. 0.234±0.008/0.214±0.020/0.203±0.023，t=2.963，2.865，and 1.073，P=0.018，0.027，and 0.317） and Myf-5（0.291±0.050/0.246±0.015/0.166±0.021 vs. 0.225±0.023/0.211±0.025/0.161±0.016，t=2.691，2.726，and 0.369，P=0.027，0.032，and 0.722） and higher mRNA expression of MyoD（5.613±0.379/3.276±0.261/1.810±0.200 vs. 4.465±0.397/2.807±0.356/1.712±0.280，t=4.679，2.377，and 0.634，P=0.002，0.048，and 0.546），with statistical signifi－cance on days 3 and 10（P<0.05）. Conclusion：LIFU can promote the regeneration and repair of chronic skeletal muscle injury in rats.