Objective: To investigate the therapeutic effect of L-carnitine on children with motor retardation. Methods: Forty children with diagnosis of motor retardation were randomly divided into a treatment group and a control group. The control group was evaluated by kinematic analysis and rehabilitation. The treatment group was given oral L-carnitine[50 mg/(kg·d−1)]. Before treatment and after 3 months of treatment, the content of free carnitine was detected by tandem mass spectrometry. The surface electromyography evaluation system, the gross motion part of the Peabody exercise development rating scale and the fine motor part were used to evaluate muscle tension, gross and fine motor ability. Results: Before treatment, the free carnitine levels in the two groups were low. After 3 months of treatment, the free carnitine in the treatment group was improved, and the control group was still low. The electromyographic signals in the system were evaluated by the surface electromyography after treatment. The time domain range myoelectric integral value (iEMG), gross and fine motor function scores were improved earlier than the control group (P<0.05). The iEMG, gross and fine motor function scores of the treatment group were compared with the control group. There are significant differences. Conclusion: L-carnitine can improve muscle tension, gross and fine motor function in patients with motor retardation.