Objective To investigate the role of electromyography (EMG) monitoring in the treatment of spastic cerebral palsy by selective posterior spinal nerve rhizotomy (SPR). Methods In 34 patients with spastic cerebral palsy who underwent SPR, EMG monitoring was applied to multiple muscle groups in the lower extremities to observe the threshold of motor response and the range of muscle contraction during stimulation of the posterior root bundle of the spinal nerve. The results showed that when the posterior root bundle was electrically stimulated, the muscle contraction could be limited to the muscle groups innervated by the nerve root segment or spread to other muscle groups ipsilateral or contralateral to it. Conclusion EMG can be useful for improving surgical outcomes, exploring the scientific nature of electrophysiological monitoring methods during surgery, and studying the relationship between electrophysiological criteria and efficacy.