Sudden weakness of the lower limbs will not walk, if it is unilateral lower limbs should be considered to be caused by acute cerebrovascular disease, generally monoplegia in cerebrovascular disease is also more common, the site will be in the parietal lobe. For example, if the weakness of the right lower limb does not walk, the lesion site may be in the left parietal lobe, we should consult the hospital in time, carry out head MRI or head CT examination, through the neurologist’s examination, to clarify the condition and then give symptomatic treatment. Weakness of the lower limbs of a single limb can also be caused by lumbar spine disease, but the patient should have a past history of low back pain and symptoms of lumbar disc compression, and will not suddenly start to suffer from the disease. If the weakness of lower limbs is double lower limb weakness and can not walk, it may be caused by the patient’s presence of hypokalemia.