The invention relates to a large-field double-wave harmonic diffractive infrared optical system. The optical system comprises a first lens, a second lens, a third lens, an aperture diaphragm, a fourth lens, a fifth lens, a sixth lens and a detector focal plane, which are coaxially arranged in sequence along the incident direction of light. The focal power of the six lenses is sequentially positive, negative, positive, negative, positive and negative. The first lens is a biconcave lens. The second lens is a biconvex lens. The front surfaces of the first and fourth lenses and the rear surface of the third lens are aspheric. The rear surface of the fifth lens is a harmonic diffractive surface. By adopting the large-field double-wave harmonic diffractive infrared optical system, wide spectrums in large-field short-wave and medium-wave ranges can be imaged simultaneously. By adoption of the harmonic diffractive design technology, the imaging and aberration correction requirements of the system are satisfied in two bands of the infrared system, and the system has good anastigmatism. The system only adopts six lenses, has an overall length of less than 50mm, and is simple in structure and light. The transfer functions in the dual band ranges are close to the diffraction limit, and the imaging quality is good.