Abstract: Several methods of the data interpolating and curve fitting are introduced. The interpolating operation of the illumination values at the wavelength intervals required by the spectral irradiance standard lamp was performed, in which the establishment of mathematical model, calculation of parameters and analysis of errors were involved. The satisfactory interpolating method and curve fitting model are obtained, and its relative deviations are close to the best uncertainty of the spectral irradiance standard lamp provided by National Institute of Metrology, which is 0.2%.