A window covering system comprises a shell, a weight member, a covering material positioned between the shell and the weight member, a control device. The covering material comprises at least one ladder, multiple slats corresponding to the at least one ladder, and at least one lifting cord, wherein the lifting cord is connected between the shell and the weight member. The control device comprises a driving module, a releasing module, and an operation module that are connected to each other. The ladder is connected to the operation module, and the lifting cord is connected to the driving module, such that the operation module drives the ladder to tilt the slats, at the same time, the releasing module is driven by the operation module to remove restriction to the driving module, hence descending the weight member.