Grating spectrometer with high spectral resolution is an important tool for detecting solar atmospheric activities. As the grating diffraction efficiency is affected by the grating incidence angle, which directly affects the energy utilization of grating spectrometer, how to accurately determine the incident angle of grating is one of the important problems in the optical design of grating spectrometer. The current methods mostly depend on the experience accumulated from engineering practice. In view of this situation, taking that multiple characteristic spectral lines can obtain higher grating diffraction efficiency as the optimization index, and taking the grating incident angle as the research object, an optimal design method for high-spectral resolution grating spectrometer is proposed, and the design of high spectral resolution solar grating spectrometer for 1 m new vacuum solar telescope (NVST) in Yunnan observatory is given.