A novel dual field of infrared optical system for uncooled focal plane Detector is purposed in this paper.The operating waveband of the system is 8~12 μm,and effective focal length is 40~150 mm.The optical configuration is based on the axial motion of a lens group along the optical axis.The optical system makes mechanism and electron simplified,which has the advantages of compact,light,portable characteristics.The optical system image quality was evaluated with the CodeV optical design software.