Wide band solar irradiance spectrometer that the wavelength coverage is from 400 nm to 2 500 nm uses fèry prism to disperse composite light, with linear array CCD controlling scan of spectrum. To achieve the high-precision spectral calibration of the instrument, asingle-wavelength laser and an OPO laser are used as light sources in the laboratory. Through thespectral scanning, the correspondence between the calibration wavelength and the CCD pixel is obtained.According to the prism and optical design parameters, the spectral calibration equations that achieve full-band spectral calibration are derived. It is verified that the spectral calibration uncertainty is better than 0.5 nm by comparing with other characteristic wavelengths. Comparing measured results with the simulation of atmospheric radiation transmission software that is named as modtran4, the measured atmospheric absorption peaks are in agreement with the simulation results. The results of calibration in the infrared wavelength region are compared with the traditional polynomial fitting method, which shows that the calibration results aresuperior to the traditional polynomial fitting method. It is proved that the calibration method is correct and the instrument design is rational.