Abstract: Based on Wien's displacement law and Planck's law, a fast measurement technique, the method of peak wavelength, was presented for directly determining the flame temperature of pulverized coal-fired boiler according to the relative spectrum of coal flame measured by fiber optic spectrometer, so as to study the effects of flame emissivity function on the temperature measurement. Taking two boilers respectively of 300 MW and 350 MW as objects of study, specific formulae of peak wavelength were proposed for measurement of the flame temperature. Results show that the peak wavelength method can be used for fast measurement of the non-gray flame like the flame in pulverized coal-fired boiler, with maximum measurement error less than 1.60%.