A head-mounted eye tracking system including an optical combiner, an eye tracker and a signal processor is provided. The optical combiner includes an optical coupler. The eye tracker is at least partially disposed on the optical combiner and is suitable for sensing an eyeball movement of a wearer. The eye tracker includes a plurality of light-emitting devices and a plurality of sensing devices. The plurality of light-emitting devices are suitable for emitting tracking beams. The plurality of sensing devices are suitable for receiving the tracking beams reflected by the eyeball of the wearer. The signal processor is signally connected to the eye tracker.