The dualband/dualFOV optical system can improve the detection capability of an IR system.The optical design theory of dualband/dualFOV telescope system was studied and a dualband/dualFOV telescope system was designed.The system can switch between the FOVsand three kinds of optical material were usedincluding GeZnSe and BaF2.The simulation result shows that the system has simple structure and fine imaging qualityand the MTF value is higher than 0.5 at the spatial frequency of 16 lp/mm.