In order to adapt to the application requirements of different field of view spectrometers, a continuous zoom medium-wave infrared spectrum imaging system based on offner scheme was designed. The front zoom system to achieve continuous zoom in the range of 60-300 mm was introduced in the system, and a grating-type offner concentric structure was used for spectral splitting and imaging. The working band was 3-5 μm, the cooled medium-wave infrared detector was used, the F#=4.0 in this system. According to the object image exchange principle and the power distribution principle, the initial structure of the front zoom system and the relay system were calculated, and the zemax software was used to optimize each subsystem to meet the design parameters. The modulation transfer function of the final continuous zoom medium-wave infrared spectrum imaging system based on offner scheme was close to the diffraction limit at a spatial frequency of 33 lp/mm, and the root mean square radius of the spot was smaller than one pixel. The design results show that the system structure is simple, and the image quality is good and meets the design indicator requirements at each focal length position and each spectral segment.