A scan driver includes: a series-connected N scan driving units; a first switch, a second switch, and a third switch. The control ends of the first switch, the second switch, and the third switch are all connected to the first node. The input ends of the first switch and the second switch receive a scan starting signal. The output end of the first switch is connected to the first scanning driving unit, the output end of the second switch is connected to the Nth scanning driving unit. The input end of the third switch receives a second high-voltage-level signal, the output end of the third switch is connected to a second node and is grounded, and the N scanning driving units are all connected to the second node. Through controlling the voltage level of the first node, the scan driver can achieve bi-directional scanning function.