This paper studies the Czerny-Turner optical structure which is used for the application in imaging spectrometers. To obtain the perfect astigmatism-corrected condition, the Czerny-Turner system has been analyzed and advanced. The basic structure of optical system is still as the traditional form which is composed by the spherical collimating mirror, the plane grating and the spherical focusing mirror. However, an off-the-shelf cylindrical lens is added after the focusing mirror to remove astigmatism differences between the tangential direction and the sagittal direction. It makes the advanced optical system presents high resolution over the full bandwidth and decreases the cost. An example of the imaging spectrum system in the waveband of 380~760 nm has been designed to prove our theory. A system owns that NA equals to 0.05, and the modulation transfer functions (MTF) of all fields of view are more than 0.59 over the broadband under the required Nyquist frequency (20 lp·mm-1). It certificates that the optical system theory can be applied to the small scale imaging spectrometer with high resolution in spectral broadband.