A damping adjustment device for adjusting a damping force to a window covering system while the window covering system is expanding, wherein the damping adjustment device comprises a damping module comprising first and second damping units. The damping force is outputted by the damping module to the window covering system when the first and second damping units generate an interaction force in between by a relative motion therebetween. An adjusting module is connected to the damping module for operating with the damping module simultaneously, wherein the damping force from the damping module is adjusted by the adjusting module altering a relative position of the first damping unit and the second damping unit when the relative motion occurs therebetween. A window covering system comprises the damping adjustment device, wherein expansion speed of a covering material of the window covering system can be effectively controlled and adjusted by the damping adjustment device.