Abstract: The yield strength and tensile strength of iron and steel materials not only decrease under the ultra-high temperature of 350℃ such as that of the thermal recovery well,but also the other physical parameters thereof change significantly,and the thermal strain rises from the secondary contradiction to the main one. Two types of the materials,i.e.,P110 and 110H studied by means of testing at room temperature and different high temperature levels. Based on the design concept of "elastic stress" and "plastic strain",the BG-TH(Thermal) heat-resistant casing is developed. The design structure is verified by the finite element analysis and the physical testing. The jointly using of the heat-resistant pipe and the heat-resistant threaded connection can improve the durability of the said casing at high temperature.