Abstract: As a spectroscopic instrument, the monochromator is used to separate mixed light into monochromatic light in the spectral responsivity calibration system of photoelectric pyrometers. To improve the uncertainty level of temperature scale extension and reproduction for photoelectric pyrometers, it is necessary to calibrate the wavelength accuracy of the monochromator output before the responsivity experiment for three commonly used photoelectric pyrometers with 660 nm, 800 nm, and 900 nm filters. In this paper, a neon atomic spectral lamp is used as a standard light source, and a spectrum analyzer is used to scan its characteristic spectral lines in the range of 600-1200 nm. Thirty-seven suitable characteristic spectral lines are selected to calibrate the wavelength accuracy of the monochromator output. The influence factors of wavelength error, such as ambient temperature, monochromator slit width, wavelength correction method, detector response, nonlinearity, and calibration repeatability, are analyzed based on the calibration results. The results show that the maximum uncertainty of the wavelength error of the monochromator at 900 nm is 0.033 nm. For the photoelectric pyrometer with a commonly used 660 nm filter, when assessing the uncertainty of the monochromator wavelength output, the temperature measurement uncertainties at 1084.62°C and 3000°C are 0.01°C and 0.28°C, respectively.