A IR zoom telescope system was designed for thermal imagery. The magnification is 4-14 and the focal length of eye piece is 25 mm. First, the frame was built up with first order optics and started design with 3rd order optics. There after, we can get the final design by optimization technique through finite ray tracing. The optical system was optimized with ray aberration or angular aberration including higer orders. Finally, The performance of the optical system was accessed by calculating the diffraction MTF from the design data. data.