A calculation model to obtain the optimal combination of Offner-Wynne imaging spectrometer parameters to balance the RMS spot radius of the chief ray over the entire field is established. On the basis of the calculation model, an Offner-Wynne imaging spectrometer is designed, and then it is applied in a short-wave infrared coded aperture snapshot spectral imager (CASSI). The optical system of the short-wave infrared CASSI is designed by a combination method of independent design and integrated optimization. The spectral smile and spectral keystone of the optical system which operates in the 900-1700 nm band are respectively less than half a pixel. The focal length of the optical system is 1200 mm, the total optical system length is 775 mm, and its average spectral resolution is 16 nm. The optical system offers the advantages of excellent imaging quality, compact optical structure, high optical transmittance, reduced spectral smile and spectral keystone.