Abstract: Disclosed are a light guide device, an optical display system, and a display device. The light guide device includes a substrate and a first diffraction structure provided at the substrate. The first diffraction structure includes a first grating. The first grating includes a plurality of first grating units provided at intervals of a first period P1 along a first vector direction u1 and at intervals of a second period P2 along a second vector direction u2. The first vector direction u1 is intersected with the second vector direction u2, the first period P1 is longer than the second period P2, forming unequal periods in two vector directions, and the first period P1 is at least 1.5 times the second period P2.