The following reasons can be considered: 1, physiological reasons, can be caused by excessive physical fatigue caused by excessive exercise, after rest with the recovery of physical strength, can gradually improve. 2, spinal cord cervical spondylosis, in the cervical spinal cord compression, patients can appear dizziness, headache, limb numbness, walking instability and other performance, especially when going up and down the stairs with a sense of stepping on cotton. 3, Other diseases may also cause weakness of the legs on the stairs, such as hypoglycemia, hypokalemia, leukopenia, anemia and other diseases.