Correcting astigmatism by using Czerny- Turner imaging spectrometer can change system focal length, which leads to the difference of magnification in tangential direction and sagittal direction of the image. The common characteristics of astigmatism correction theories of Czerny- Turner imaging spectrometers (using cylindrical mirror and toroidal mirror) are analyzed. And the correction formulas, methods of anamorphose and their common characteristics are given. The validity of correction formula of anamorphose are verified with theoretical calculation, ray tracing simulation, and actual measurement. Meanwhile, this method of image correction is useful to the anamorphose correction research of off- axis structure dispersion imaging spectrometer in other operating conditions of collimation light.