The design of an infrared multiple FOV optical system with a MWIR/LWIR dual-band staring focal plane array detector was introduced. Wide medium narrow FOV was realized by inserting different sets of lens groups in narrow optical path. The harmonic diffraction theory and aspheric design method were used in the aberration balance. The operating wavelength region is 3 to 5 μm and 7.7 to 9.5 μm, F-number is 3, and zoom ratio is 18∶1. The results indicate that the modulation transfer functions (MTF) of all FOV are approaching to diffraction limit, 70 percent medium-wave infrared encircled energy and 60 percent long-wave infrared encircled energy are concentrated in one pixel of detector. Moreover, it could obtain well optical performance in all temperature range. The dual-band optical system could be widely applied in military and civilian opto-electronic detective fields.