The calibration of the temperature and effective wavelength must be carried out before multi-wavelength pyrometers application. The current calibration method of the effective wavelength for the multi-wavelength pyrometers is the pyrometer wavelength function (PWF) method. However, for the actual calibration of the fiber-optic multi-wavelength pyrometer, the signal is too weak to obtain effective wavelength by the PWF. Therefore, a new calibration method based on optimization function for effective wavelength is proposed in this paper. The core idea of the innovation is to transform the effective wavelength calibration into an optimization problem, in which the effective wavelength can be solved directly by the MATLAB software using the temperature calibration data. Comparing with the PWF, the presented new method not only provides a novel way to obtain effective wavelength, but also avoids time-consuming due to the complicated process from the wavelength calibration. Finally, simulation and experimental results verify that the proposed method is effectiveness by using the function fmincon and minconPS from MATLAB software, in which the fmincon function is superior to the minconPS function for the efficiency and anti-noise performance.