A top-down bottom-up window covering has a headrail, a middle rail, a bottom rail, a lifting control structure installed at the headrail, and a covering structure installed between the middle rail and the bottom rail. The lifting control structure controls a first rotating shaft and a second rotating shaft to respectively receive or release a first cord and a second cord. The first cord drives the middle rail to move, and the second cord drives the bottom rail to move. A one-way clutch and a pre-stress unit are further provided at the headrail. When the bottom rail pushes the middle rail to move upward, the one-way clutch breaks a link between the first rotating shaft and the lifting control structure. Consequently, a driving force generated by the pre-stress unit immediately drives the first rotating shaft to receive the first cord to keep the first cord taut.