Thermal characterization of high-power Lighting Emitting Diode (LED) device was reported, utilizing finite element software ANSYS with thermal stress analysis based on the thermal stress theory, and the transient temperature and stress field were obtained. The thermal stress, displacement and shear stress distribution on the path which was parallel with X axis at the top of LED substrate were calculated. The simulation results indicated that the maximum von mises stress was at the corner of the thermal sink and die attach, and the maximum displacement was located at the edge between the lens and the thermal sink. The maximum shear stress was concentrated at the corner region. The numerical study that was carried out with LED base center to understand the temperature distribution by FEM technology was experimentally calibrated. Finally, variation of the maximum temperature and maximum thermal stress with thermal conductivity of various materials was considered. The results are of great importance to the high-power LED package.