An inductor, a power factor correction circuit, and a power supply system. The inductor includes a coil winding and a magnetic core. The magnetic core includes a first outer magnetic core, a second outer magnetic core, and a winding unit. The first outer magnetic core and the second outer magnetic core are disposed opposite to each other in a first direction, the winding unit is disposed between the first outer magnetic core and the second outer magnetic core, and the coil winding is disposed around the winding unit. The winding unit includes a magnetic core middle column and at least two air-gaps distributed in the first direction. The inductor can improve the operating efficiency of the power factor correction circuit and can optimize efficiency of the power supply system in the light load phase.