The invention provides an infrared broadband antireflection microstructure comprising a substrate, a nanostructure array layer and a low-refractive-index layer which are arranged from the bottom to the top in turn. The nanostructure array layer is provided with nanostructures which are perpendicular to the main axis of the surface of the substrate, and the cross section of the nanostructures has atriangular, conical, parabolic or Gaussian isogradient structure. A layer of low-refractive-index material is added to the nanostructure array, and the low-refractive-index layer is realized by the ion beam sputtering deposition technology or the electron beam evaporation ion beam auxiliary deposition technology so as to avoid water absorption. The thickness of the low-refractive-index layer is adjusted so that the broadband antireflection effect of the nanostructure array layer can be enhanced, high transmittance of broadband range can be realized and the transmitting curve is flatter.