Temperature measurement technique using thermographic phosphors can measure the accurate 2D temperature field even in the harsh environment such as high temperature and high pressure, because it is not affected by oxygen quenching or pressure up to 10 bar. Phosphor thermometry is based on the luminescence-changing characteristics with temperature. Both a simple and fast analytical method and interrogation window concept can reduce evaluation time were described to analyze time-resolved phosphorescence signal. Decay-slope method could analyze the temporal response of phosphors using few initial phosphorescence data, so the number of data which consider is smaller than conventional lifetime analysis. As a result, the decay-slope method improved computation time more than 20 times faster than that of the lifetime analysis.