A diffractive/refractive long wavelength infrared (LWIR) staring imaging system is designed to meet the commercial requirements. In this system the F-number is 1,waveband is 8～12 μm ,field of view is 12°, total track is 140 mm and the materials of the total two lenses are Germanium. The diffractive optical element (DOE) is fabricated on the convex of the second lens,and the DOE can be fabricated by diamond turning technology. The imaging quality is analysed that the Modulation Transfer Function (MTF) approaches the dilfraction limit and the chromatic aberration is better corrected compared with the refractive system.