The knee reflex is a common examination reflex of the nervous system and is a common operation to check whether the low-level central response is normal. The procedure is as follows: Have the patient sit in an upright position with the lower extremities relaxed, then the examiner holds the patient’s lower extremities in his or her hands and gently taps the biceps femoris tendon with a percussion hammer and can see the lower leg kicking forward, which is a normal knee reflex. When the nervous system is malfunctioning or dysfunctional, the knee reflex can disappear, which means that the biceps femoris tendon is tapped and there is no forward kick of the lower leg. If the nervous system is dysfunctional and loses control of the knee reflex, it can cause a hyperactive knee reflex, which means that when the biceps femoris tendon is struck with a percussion hammer, the lower leg can be seen to kick forward with force and the strength and amplitude of the kick is beyond the normal level.