With the in-depth research in the physical process of solar activities, the demand for the performance of solar extreme-ultraviolet imaging spectrometer is increasing. One important method of designing high-performance sun extreme-ultraviolet imaging spectrometer is to use the holographic varied line spacing grating. The design method is presented in this paper as follows. The initial optical structure of the system is designed firstly. Then the grating whose aberration is small is calculated based on holographic varied line spacing grating′s optical path difference theory and universal global optimization of 1stopt software. The entire system is modeled and optimized with optical design software Zemax finally. A design example is given with the working band of 17～21 nm, the field of view of 2400″, the spatial resolution of 0.6″, the spectral resolution of 0.00225 nm/pixel, and the length of about 2 m. In the spectral range, the root mean square radii in spatial direction and spectral direction and the modulation transfer function in the cutoff frequency range all satisfy the requirement.