Abstract: The present invention aims to provide a light guide apparatus based on diffraction gratings. The apparatus comprises a light guide plate (11) comprising a first diffraction grating (13) located on a first surface of or inside the light guide plate (11); a first light source (12), coupled to a first side of the light guide plate (11); wherein the first diffraction grating (11) is configured to extract the light generated by the first light source (12) from the first surface of the light guide plate (11). Since the first diffraction grating (13) is invisibly small, users hardly notice any change of the light guide (11). When the light guide apparatus of the present invention is used as a book reader, the dark area produced when lifting the book reader in a direction away from the objects to be read is smaller than that of existing light guide apparatus based on microstructures, since the light exit angle is relatively small when using a diffraction grating.