A cordless window blind structure is provided. A movable seat having a pulley block and a cord-winding assembly is disposed within a head rail of the cordless blind. The pulley block is connected to a lift cord wound through a first positioning element, so as to control the opening and closing of a blind body. And the cord-winding assembly has a cord winder attached to one end of a retrieving cord and a torsion spring. The other end of the retrieving cord is fastened either on the head rail, the movable seat, a second positioning element, or an end cap. The structure of the second positioning element is resembled to the first positioning element. By taking one end of the retrieving cord as a pivot, the movable seat moves laterally therealong the head rail by a restoring force generated through the torsion spring.