The appearance of one leg thick and one leg thin is mainly a clinical manifestation of muscle atrophy caused by various reasons. However, there are many kinds of clinical diseases that cause muscle atrophy, so patients need to be investigated one by one according to their own diseases. Firstly, if the patient has cerebrovascular diseases such as cerebral infarction or hemiplegia caused by various central nervous system reasons such as intracranial tumor compression, such manifestations can occur. Secondly, some peripheral nerve injuries can also cause such symptoms, such as lumbar disc herniation compressing the sciatic nerve, pediatric paralysis patients, lumbar spine or lower limb muscle injuries caused by trauma. These patients can first go to the hospital for electromyography to identify the site of nerve injury and then take targeted treatment.