In the multi-wavelenth temperature measurement system, the spectral emissivity is assumed to be a wavelength or temperature model to solve the true temperature. Because of the uncertainty of the model assumption, spectral emissivity model is inconsistent with the variation rule of the actual spectral emissivity, which will cause larger inversion error. In addition, the poor universality of the mathematical relationship between the emissivity and wavelength or temperature, especially the measured radiator is changed, the relationship will cease to exist. In order to the obtain the true temperature, the optimization idea is introduced into the method for the first time, and a single objective minimization optimization method(SMO) was established to complete the inversion of true temperature. The new method does not need to establish a model between spectral emissivity and wavelength or temperature, and has a certain universality. Compared with the second measurement method(SMM), the inversion speed of the proposed method was increased over 95% in the same initial conditions.