The paper analyzes the advantages and disadvantages of dispersion method between prism and grating from some different points of view. The result indicates that the prism is more suitable for space-borne high resolution hyper-spectrum imager. The transmission efficiency of spectrometers with prisms is 95.24%(VNIR) and the diffraction efficiency of grating is between 60% and 70%. Moreover, the stray light of spectrometers with prisms is 10－4 and that of spectrometers with grating is 10－2. Furthermore the spectrometers with prisms is better than the spectrometers with grating between 0.4 －2.5 .In the dispersion linearity aspect, the spectrometers with grating are linear. The nonlinear problem of shortwave for spectrometers with prisms can be solved through double-prisms. Spectrometers with prisms are more reliable than Spectrometers with grating. In the spectrum bandwidth and cost aspect, Spectrometers with prisms and grating are equivalent.