Image slicer is an important optical device in astronomical observation spectrometer. It can effectively improve the resolution and energy transmittance of the instrument. The image slicer can divide the circular image spot into strips and arrange the strips in a straight line, so that all the image spots can pass through the spectrometer slit. Image slicers are commonly used in astronomical observation spectrometers to help instruments achieve high spectral resolution with medium apertures. Image slicers can be divided into 4 categories according to their working principles. Among them, Bowen-Walraven type is the most widely used image slicer type. Coherent dispersive spectroscopy is a technique that combines an interferometer and an intermediate resolution spectrometer. It measures the phase change of the interference fringes of the stellar spectral lines after the Doppler frequency shift, and calculates the radial velocity change of the star and the mass of the planet. Since the phase difference has a certain amplification factor relative to the wavelength offset, when the spectral resolution is the same, the radial velocity detection accuracy of the coherent dispersion technique can be greatly improved compared with the traditional echelle grating method.This paper is based on the coherent dispersive spectrometer used to detect exoplanets by the radial velocity method. The radial velocity detection accuracy is expected to be less than 1 m/s, and the detection target is K/M dwarf stars. The structure of the coherent dispersion spectrometer consists of collimating mirror, Sagnac interferometer, imaging mirror group, image slicer, relay mirror group, slit, dispersion grating and CCD. The working spectral range of the spectrometer is 660~900 nm, the system transmittance at the center wavelength is about 0.4, and the spectral resolution is 0.03 nm. In order to meet the requirements of energy utilization and spectral resolution, the system needs to use the image slicer to realize the target surface multiplexing of the CCD and the reasonable matching of the numerical aperture. Therefore, setting a reasonable number of segmented images and the F number of the imaging lens group to achieve a good segmentation effect is of great significance to the improvement of system performance.In order to reduce the influence of imaging defects on the system, two design schemes of the image slicer are modeled and calculated in this paper. This paper also studies the relationship between the thickness of the reflective cavity and the incident angle and the defocusing and object point repetition, and deduces the general design formula of the thickness of the optical reflective cavity, which provides an important reference for the design of the image slicer. In addition, for the coherent dispersive spectrometer system used for exoplanet detection, this paper simulates the defocus and object point repetition under different F numbers and segmentation numbers. By analyzing the simulation results, the following conclusions are obtained: 1) With the increase of the F number and the number of divisions, the defocus amount increases significantly, and the defocus phenomenon becomes more obvious. 2) The phenomenon of object point repetition appears in all simulation results, which is determined by the design principle and cannot be avoided. 3) The design results of the two design schemes are relatively similar. Since the optical path in the Bowen?Walraven type design is propagated through the glass medium, the defocus amount is larger than that of the simplified type. The ratio of the diffuse spot diameter to the image spot diameter is the same for both methods. Based on the comprehensive simulation effect, and considering the requirements of the coherent dispersion spectrometer system, it can be considered that the imaging defects are relatively balanced and the energy loss is less when the star image is divided into 4 under the condition of F/24, which is a relatively suitable solution. In addition, since the defocus amount of the simplified type is smaller, and only the flat mirror needs to be processed, the cost is lower, so the simplified design scheme can be adopted.The work of this paper plays an important role in achieving the expected performance of the instrument, and provides a reference and application reference for other high-resolution spectrometers to determine system parameters. At the same time, the work of this paper provides a general design idea for Bowen?Walraven and simplified image slicer design, which is instructive for optimizing the design process of image slicer.