Aim at traditional contactless true temperature inversion algorithm has the problems of slow inversion speed and low accuracy,a new constrained true temperature inversion algorithm (CTTIA) based on luminance temperature model is proposed.In the whole modeling process,it is found that emissivity and luminance temperature have internal relations:the universal law from luminance temperature to emissivity or from emissivity to luminance temperature.The simulation results show that when the number of emissivity samples is huge,the CTTIA can not only provide theoretical guidance for the experiment,but also greatly improve the selection efficiency of emissivity samples.Nine wavelength channels are built to measure and calculate the measured objectives at 1 800 ℃ and 2 000 ℃.The results show that the accuracy of the CTTIA is almost the same as that of the second measurement method (SMM),and the inversion time is reduced to 82%.It illustrates that the research of this method is very critical and important,has great research value.