Thermal infrared remote sensing is one of the focuses in remote sensing investigations all over the world, and the retrieving of land surface temperature is an important research field. This paper has analyzed the difficulties in the inversion process and summed up several methods for estimating ground absolute emissivity. Three inversion methods and their main merits and shortcomings, their application fields and conditions are described, and the future development trends as well as the key points in the inversion of land surface temperature are also dealt with in the end of this paper.