A window covering system, comprising: a headrail, a bottom rail, a covering material, and a control unit, wherein the covering material is positioned between the headrail and the bottom rail, and the control unit is positioned outside of the headrail; and a first rotating unit positioned within the headrail, wherein the first rotating unit (20, 31) is configured to be driven to rotate in a first direction when the bottom rail descends to expand the covering material; and a locking device (23, 37) coiled to the first rotating unit (20, 31), wherein the locking device (23, 37)comprises a fixed end (231, 371) and a free end (232, 372), and the fixed end (231, 371) is fixed relative to the headrail, and wherein the locking device (23, 37) is configured to provide a restriction force to the first rotating unit (20, 31) in order to restrict the first rotating unit (20, 31) from rotating in the first direction, as well as to restrict the bottom rail from descending; an actuating device (25, 38) comprising a pushing part (251, 381), which is positioned corresponding to the free end (232, 372) and configured to operate with the control unit simultaneously, characterized in that the control unit is configured to drive the pushing part (251, 381) of the actuating device (25, 38) to push against the free end (232, 372) of the locking device (23, 37) to move in orderto remove the rotation restriction to the first rotating unit (20, 31) by reducing the restriction force provided by the locking device (23, 37) to the first rotating unit (20, 31); when the rotation restriction to the first rotating unit (20, 31) is removed, the bottom rail descends by gravity to drive the first rotating unit (20, 31) to rotate in the first direction; and comprising a rod (24, 30) connected to the control unit and the actuating device (25, 38), wherein, when the control unit drives the rod (24, 30) to drive the pushing part (251, 381) of the actuating device (25, 38) to push the free end (232, 372) of the locking device (23, 37) to move in order to remove the rotation restriction to the first rotating unit (20, 31), the bottom rail descends by gravity to drive the first rotating unit(20, 31) torotate in the first direction to expand the covering material. a headrail, a bottom rail, a covering material, and a control unit, wherein the covering material is positioned between the headrail and the bottom rail, and the control unit is positioned outside of the headrail; and a first rotating unit positioned within the headrail, wherein the first rotating unit (20, 31) is configured to be driven to rotate in a first direction when the bottom rail descends to expand the covering material; and a locking device (23, 37) coiled to the first rotating unit (20, 31), wherein the locking device (23, 37)comprises a fixed end (231, 371) and a free end (232, 372), and the fixed end (231, 371) is fixed relative to the headrail, and wherein the locking device (23, 37) is configured to provide a restriction force to the first rotating unit (20, 31) in order to restrict the first rotating unit (20, 31) from rotating in the first direction, as well as to restrict the bottom rail from descending; an actuating device (25, 38) comprising a pushing part (251, 381), which is positioned corresponding to the free end (232, 372) and configured to operate with the control unit simultaneously, characterized in that the control unit is configured to drive the pushing part (251, 381) of the actuating device (25, 38) to push against the free end (232, 372) of the locking device (23, 37) to move in orderto remove the rotation restriction to the first rotating unit (20, 31) by reducing the restriction force provided by the locking device (23, 37) to the first rotating unit (20, 31); when the rotation restriction to the first rotating unit (20, 31) is removed, the bottom rail descends by gravity to drive the first rotating unit (20, 31) to rotate in the first direction; and comprising a rod (24, 30) connected to the control unit and the actuating device (25, 38), wherein, when the control unit drives the rod (24, 30) to drive the pushing part (251, 381) of the actuating device (25, 38) to push the free end (232, 372) of the locking device (23, 37) to move in order to remove the rotation restriction to the first rotating unit (20, 31), the bottom rail descends by gravity to drive the first rotating unit(20, 31) torotate in the first direction to expand the covering material.