To study the effect of spectral curvature on the acquired radiant signal by imaging spectrometer with prism dispersion, the errors of acquired signal between with spectral offset 0.01, 0.05, 0.1d (d is pixel dimension) and without spectral curvature was calculated by combining with the dispersive characteristics of composite prism in Visible-Near Infrared VNIR (400~1 000 μm). The experimental results indicate that the scene radiant signal acquired by imaging spectrometer with spectral line bend exhibits distinct errors at the edges of atmospherical absorption bands compared with no spectral curvature, and the normalized signal errors increase with the spectral offset. When spectral resolution increases, there are distinct signal errors near some weak atmospherical absorption peaks. These results reported here suggest that spectral curvature should be no more than 0.3 nm for imaging spectrometer with 10 nm resolution.