Abstract: The stress condition of the thermal well casing string is more complicated than that of ordinary well casing string.Based on analysis of relevant information available, rule of the effect by thermal well temperature on the casing property values is discussed.A regression model is established for the empirical correlations of casing yield-strength, Young's modulus, and linear expansion coefficient vs temperature.Furthermore, several problems encountered with during field designing of thermal well casing string in the recent years are discussed, and certain key issues are emphasized for the said design.Take into account the effect of temperature on casing property values, examples of calculation of the pretension for the thermal well casing are made, providing valuable information to casing string designers.