The first and most common cause of weakness in one leg is lumbar disc herniation, in which the herniated disc or nucleus pulposus compresses the nerve root, resulting in radiating pain in the muscles of the innervated area. If the nerve is compressed for a long time, ischemic degeneration and necrosis will result in muscle atrophy and numbness of the innervated muscles, which will lead to weakness of one side of the limb and difficulty in walking. In this case, it is recommended to improve the lumbar spine MRI or CT examination, to clarify the segment of the herniated disc and the degree of herniation, if the lower limb weakness has occurred, it is recommended that early surgical treatment. The second reason is to pay attention to whether there is craniocerebral lesion, generally speaking, cerebrovascular accident usually leads to one side of the limb weakness, mainly including one side of the upper limb and lower limb numbness, muscle weakness, walking difficulties. In this case, CT or MRI examination of the brain should be perfected as soon as possible, and once the diagnosis is clear, it should be treated as soon as possible.