The advantages of small aberration and high transmittance exist in Dyson prism imaging spectrometers studied at home and abroad. The purpose of this paper is to improve the dispersion uniformity of the Dyson prism imaging spectrometer. By analyzing the dispersion law of prisms made of different materials, this paper chooses fused silica and CaF₂ materials to form achromatic prism group, and uses super-ring reflecting surface and lens group to correct other aberrations. Through optimization, a Dyson prism imaging spectrometer with a slit length of 80 mm and uniform dispersion is obtained. At the same time, the structure of double-objective lens and the means of splicing slits are chosen to meet the overall requirement of 200 km swath. The results show that the resolution is 10 nm in 400-2500 nm band and the slit length is 80 mm. The design value of the optical system is under the 25 lp/mm cut-off frequency, and the modulation transfer function is larger than 0.6. According to the spectral position of the image surface after dispersion of each wavelength, we obtian that in the range of 400-1200 nm, the fitting accuracy between the dispersion curve and the fitting line increases from 0.88 in the case of a double material prism to 0.94 in the case of a single material prism, which greatly improves the dispersion uniformity.