At present, Multispectral pyrometer used in high-temperature measurement has already had high resolution and high signal to noise ratio. However, the non-source temperature (higher than 3 000 ℃) calibration falls far behind the development of multispectral pyrometer and has already seriously hindered the precision and application range of the pyrometer. In order to break through the limitation of calibration of non-source temperature, a new calibration method was put forward in the present paper. The temperature-voltage (T-U) model was formed based on power function where output voltage U of the multispectral pyrometer was derived from its corresponding known temperature point. Based on the model, derivative least square method was used to obtain the parameters of the model to realize the non-source temperature calibration. Both theoretical and experimental data proved the efficiency and precision of the calibration method. In addition, within the spectral range of high-temperature measurement pyrometer (0.4~1.1 μm), the range of non-source temperature calibration with precision better than 3‰, 1% and 3% respectively have been divided theoretically.