The parameters and property of Offner imaging spectrometer were studied according to eliminating aberration structure. The calculating equations of measurable range of wavelength, linear dispersion and spectral resolution were deduced by geometry method based on eliminating aberration structure of Offner imaging spectrometer; the relationship of resolution and each factor were analyzed, these factors including width of entrance slit, convex grating resolution and pixel size of detector. When the system aberration was to be ignored, the spectral resolution could be enhanced by decreasing width of entrance slit , this conclusion was verified by imaging experiment. The techniques and methods of improving spectral resolution were summarized, the tradeoff balance between each parameter and spectral resolution were considered. The final conclusion was as follow: the resolution of Offner imaging spectrometer was determined by the lowest resolution of the entrance slit, convex grating and pixel size of CCD.