The present invention provides a method for setting elastic threads in a ligation device and an automatic elastic thread ligation device using the method. At least one elastic thread (2) is arranged along the outer wall of a barrel (3) of the ligation device, and an annular sleeve (21) with an adjustable aperture and formed at the front end of the elastic thread (2) is sleeved on the outer wall of the front end of the barrel； a traction thread (26) on the ligation device is connected with the annular sleeve (21) of the elastic thread (2), and when the traction thread (26) is pulled, the traction thread drives the annular sleeve (21) to move towards the orifice of the barrel (3), until the annular sleeve is disengaged from the orifice； a force bearing part of the annular sleeve (21) at the front end of the elastic thread is propped forwards, meanwhile, the tail end of the elastic thread (2) is pulled backwards, and the countertraction between the two acting forces leads to a gradual decrease of the aperture of the annular sleeve (21) at the front end of the elastic thread (2). In the automatic elastic thread ligation device, rubber rings are replaced by the elastic threads, after the annular sleeve at the front end of the elastic thread is pulled by the traction thread and pops up from the orifice of the barrel, the aperture of the annular sleeve can be decreased gradually by pulling the tail end of the elastic thread until the aperture becomes approximately zero, so that tighter ligation of the target tissue can be achieved, and an ulcer surface is extremely small after the target tissue becomes necrotic and falls off, so that the probability of postoperative bleeding is lowered.
