This trial is primarily aimed to compare the effect and safety of electro-acupuncture and prucalopride for severe chronic constipation: if the short-term effect of electro-acupuncture is no inferior to prucalopride? Besides, the investigators will also mainly confirm the superiority of electro-acupuncture: if the effect of electro-acupuncture can last for 3~6 months? Then, assess the patients' acceptance of electro-acupuncture.