A unidirectional coupling damping pulley includes a threaded central spindle extending into a pulley hub, a friction stopper ring and a positioning sleeve pressed against the inner wall of the pulley hub, a protruding ring formed on the outer diameter of the central spindle, in which the central spindle is sleeved with a damping washer forming a step on one side of the damping washer, the central spindle is sleeved with a damping spring, the damping washer is sleeved and in rotation fit with a friction sliding ring, a friction spring is sleeved around the damping spring, the friction spring locks up with the friction stopper ring and the friction sliding ring through friction, and the friction spring can be separated from the friction stopper ring and the friction sliding ring alternately.