Thermocouple protection tube according to the material classification metal: high mechanical strength, good thermal performance, application is very broad. Thermocouple protection tube: not much at above 1000 ℃ temperature measurement using, heat resistant performance is good, shock resistance is poor, poor thermal conductivity. Metal ceramic protection tube: due to the metal materials, high mechanical strength, but not high temperature resistant; Nonmetallic material high temperature resistant, low mechanical strength. Made by powder metallurgy method of metal ceramic protection tube, which has high temperature resistant performance and has good mechanical strength, has a good application prospect, and can be widely used in steel, iron and high temperature salt bath furnace and other harsh environment. Thermocouple protection tube selection considerations of the measured medium temperature, atmosphere, flow velocity, corrosion resistance, the thickness of the pipe, wall thickness, length, air tightness, thermal shock and chemical adaptability, under pressure, stress, response speed and cost performance. We can according to the actual situation, choose the appropriate protection tube material. The selecting principle of thermocouple protection tube is according to the technical indicators are combined with the actual situation, to select the scheme. In the practical work, we can according to experience, the manufacturers instructions or manual, protecting tube materials quickly. Must pay careful attention to use the materials with various specific situation.