The degree of pain at night after fracture is more serious than the degree of pain during the day, mainly due to the sympathetic and vagal excitability changes. When the limb will be obviously swollen after the fracture, due to the swelling of the fracture and produce more obvious pain, when the daytime sympathetic excitability increases, so the degree of pain tolerance increases, in the daytime pain is easy to tolerate, will not be too serious. However, at night the vagus nerve excitability will increase and the sympathetic nerve excitability will gradually decrease, so it is more sensitive to pain, making the pain sensation increase, so it will lead to more pain at night.