Sudden weakness of legs may be caused by peripheral neuropathy, central neuropathy, electrolyte disorders and so on. 1. Peripheral neuropathy: If the peripheral nerves are compressed, acute onset due to external force or change of body position may cause sudden weakness of legs, such as lumbar disc herniation, lumbar spondylolisthesis and so on. 2. Central neuropathy: the brain belongs to the higher center, and the lesion of the higher center will lead to the signal cannot be transmitted to the receptors of the limbs correctly, and the receptors cannot receive the correct signals, resulting in the inability to carry out the normal contraction movement, and the above mentioned symptoms may occur, such as cerebral hemorrhage, cerebral infarction, and so on. 3. Electrolyte disorders: when electrolyte disorders are caused by various reasons in the body’s internal environment, the concentration of potassium and sodium ions inside and outside the cell will change, resulting in the inability of the cell to maintain normal excitability, and the above symptoms may also occur. Sudden weakness of the legs may also have other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.