An X-ray detector includes a substrate, plural signal lines, plural scan lines, plural sensing units, and a first active device. The signal lines are disposed on the substrate. The scan lines are disposed on the substrate and intersecting with the signal lines. The sensing units are electrically connected to the signal lines and the scan lines. The first active device has a first terminal, a second terminal, and a control terminal configured to modulate a conduction between the first terminal and the second terminal. The first terminal of the first active device is connected to a first one of the signal lines, and the second terminal of the first active device is connected to a second one of the signal lines.
