A radiant cooling optical filter, comprising a substrate. A single surface of the substrate is polished, a metal reflective plate is provided on the rough surface, and an intermediate layer and a top layer are provided in sequence on the polished surface of the substrate; the intermediate layer comprises a layer A and a layer B arranged alternately; the thickness of each of the later A and the layer B is 50-400 nm; the layer A is made of silicon oxide or aluminum oxide, and the layer B is made of titanium dioxide, silicon nitride, or silicon carbide; the top layer is made of ytterbium fluoride, yttrium fluoride, or zinc sulfide; the intermediate layer and the top layer together constitute a multi-resonant absorption enhancer in an atmospheric transparent window (a 8-13 um wave band). Compared to a conventional optical filter, the optical filter can work under strong light for a long time, and can implement passively radiant cooling.