To satisfy the requirements of a high-resolution hyperspectral imager with a large relative aperture and a wide spectral region, a new type plane grating spectrometer was proposed and designed based on double Schwarzschild structures. The astigmatism-correcting condition was derived based on the theory of geometrical aberration. The initial parameter computing was programmed by using Matlab software. As an example, an optical system for the plane grating spectrometer with a relative aperture of 1/2.5 operating in 350—1 000 nm was designed. The initial parameters were computed using proposed Matlab program, then the ray tracing and optimization for the spectrometer system were performed with ZEMAX-EE software. The analyzed results demonstrate that the spot radius(Root Mean Square, RMS) is less than 8.2 μm in the whole working waveband (from 350 nm to 1 000 nm), the astigmatism-corrected is realized, and good imaging quality is obtained in a wide spectral region with a large relative aperture. Obtained data satisfy the requirements of design specifications, and prove the feasibility of the new type plane grating spectrometer base on double Schwarzschild structures. It has extensive application prospects in spaceborne and airborne hyperspectral remote sensing fields.