As acquiring spectral response function by experimental method is always time limited and with a complicate process,a simulation of spectral response function and spectral resolution based on huygens point spread function was suggested. Taking into account the effects of optical aberration and diffraction,the fine spectral response function curves and spectral resolution at any nominal wavelength of the full spectral range can be calculated as early as in the design phase. A grating spectrograph with a spectral range from 1 000 nm to 2 500 nm was proposed for illustrating the simulation process. With a geometrical ray tracing method as a comparison,the spectrograph′s spectral response function at single wavelength and full spectral range are simulated by huygens point spread function method. The results demonstrate that the full width at half maximum of spectral response function acquired by huygens point spread function method is greater than the result of geometrical ray tracing method at any wavelength. The relative deviation changes from 2% to 5% for the full spectral range. Both optical aberration and diffraction affect the result of huygens point spread function method. At last,the comparison of spectral response function curves acquired by the two methods is shown with logarithmic scale for the y-axis. The results show that the effect of diffraction is dominant when relative response between 10－2 and 10－5 and can be neglected below 10－5. The uncertainty of the simulated process for the spectrograph with a 10nm spectral resolution is 0.025 nm.