In order to eliminate spectral line curvature of plane grating and prism imaging spectrometer, a novel approach by combining prism-grating (P-G) with the compensation of lens′ distortion is presented. The spectral line curvatures of prism and grating and spectral curvature of compound P-G device are calculated, respectively. The character of spectral line curvature and spectral curvature are analyzed, then the compound P-G device and imaging spectrometer with eliminating spectral line curvature are designed. The optimized optical system has a spectral resolution better than 2 nm and the root mean square (RMS) spot radius is less than 8 μm. Moreover, both the spectral line curvature and spectral curvature of system are less than 2 μm. It is proves that compound P-G device′s spectral line curvature and spectral curvature of the full-wide working wavelength can be eliminated with the compensation of lens′ distortion. It is concluded that the imaging spectrometer with P-G dispersing device shows a spectral line curvature less than 1/4 pixel of the detector, which meets the use request on the premise of imaging quality.