Thermal stress of steam turbine rotor (STR) is a fatal factor which greatly influences its fatigue life. To calculate the thermal stress field, academicians from all over the world have done a lot of research, which contains mathematical methods and numerical methods. In the process of calculating thermal stress mathematically, the thermophysical properties of rotor material are paramount influencing factors. The sensitivity of STR thermal stress on thermophysical properties of rotor material has been analyzed in this paper. Six independent thermophysical parameters of steel for rotor are concerned, including density, special heat, thermal conductivity, coefficient of linear expansion, Young's modulus and Poisson's Ratio. Calculation results show that rotor's thermal stress is very sensitive to thermal conductivity, coefficient of linear expansion and Young's modulus. The sensitivity coefficients of these properties are all around 1, which means the change rate of thermal stress is approximately tantamount to that of those properties. Besides, the sensitivity of thermal stress either to density or to special heat is moderate, their sensitivity coefficients are around 0.7. Thermal stress rotor is less sensitive to Poisson's Ratio, which is only approximately 0.3.