Because harmonic diffractive optics elements has special achromatism, athermalization and arbitrary phase modulation characteristics, an infrared detection system method with dual spectrum and wide temperature range was presented based on the most advanced infrared dual color detector which had a format of 320×240 and the pixel pitch of 30 μm. A hybrid refractive/harmonic diffractive infrared detection system with dual spectrum and wide temperature range was designed. The working wavelength range was 3.8～4.2 and 8.8～11.2 μm. The system was only consisted of three lenses, including one aspheric surfaces and a harmonic diffraction surface, which made the system have compact structure and light weight. In the temperature range -120～200 ℃, the RMS radius of spot diagram in 3.8～4.2 and 8.8～11.2 μm was 19.07 and 17.75 μm respectively, which is less than the pixel size of infrared detector with 30 m, the enclosed energy in 30 μm, the enclosed energy in 3.8～4.2 and 8.8～11.2 μm is 88.7% and 82.4% in two pixel size. The method and structure was convenient and predominant. It was proved that the design was feasible.