Switch-zoom optical system with F-number of 0.9 is designed by optimizing the multi aspheric surface to match a array uncooled long-wave infrared focal detector with high resolution of 1 280 × 1 024 and small pixel size of 12 × 12 μm, where its field of view could change from 36.3° to 20.64° to satisfy the special needs of discovering and identifying target, respectively. By introducing multiple aspheric surfaces, the modulation transfer function (MTF) is greater than 0.3 at the Nyquist frequency of 42 lp/mm, which greatly improves the contrast and resolution of the system compared to that of the spherical system. Compared with previous work, this system owns better properties and avoids complex binary surfaces.Furthermore, the design results show that the MTF of any state is greater than 0.2 at 42 lp/mm in the temperature range of 0~40 ℃. Our work pave the way for wide scan detection and accurate target recognition. The system is based on the staring focal plane infrared detector with super large area array scale and ultra-small pixel, which can meet the imaging requirements and can search and capture the target. It can be combined with the airborne system to form the airborne infrared search and tracking system, which has certain significance for the development of airspace surveillance, threat judgment, detection of incoming missiles, automatic search and tracking of targets.