Temperature and emissivity are the most important parameters in thermal remote sensing. A thermal temperature and emissivity separation algorithm based on Wien approximation and Alpha derived emissivity method (ADE) are proposed. This method corrected the Wien approximate based on the mathematical principle, and calculated the spectral shape using ADE to identify the band which had the maximum and minimum emissivity, then deduced the relationship of each band’s emissivity after the correction of Wien approximate and derived the actual emissivity using this relationship and MMD model. For choosing better MMD model, this article compared the precision of two MMD model and applied the module which has higher precision in the algorithm. From the comparison with another method, the algorithm proposed here had higher precision and better stability. The inversion error of temperature is less than 1 K while which of emissivity is less than 0.015.