In this paper, for the measured surface with the characteristics of continuous radiation, we put forward the general model of the spectral emissivity with non- dimensional wavelength. In the analysis process, based on the Taylor series expansion, we theoretically discuss the applicable conditions of the model. Further, introducing the concept of the non-correlative spectrum functions in colourometry, the principle of primary spectrum pyrometry is established. And the application of primary spectrum pyrometer is illustrated in a specific example.
