Based on performance and application characteristic of acousto-optic tunable filter (AOTF) and the detector, a fore zoom optical system for AOTF spectra camera is designed which works on medium wave. The optical system adopts hybrid diffractive-refractive model and six lens to achieve a 12× continuous zoom configuration and ZEMAX software is used to optimize the optical system and assess the image quality of the system. The results show that the Modulation Transfer Function (MTF) of the system approaches to diffraction limit across the whole brand at spatial frequency16 lp/mm, encircled energy is greater than 90%. It is demonstrated that the system can apply in the field of infrared spectral imaging analysis and infrared target detection and recognition.