There are four kinds of commonly used thermometers in air separation plant: industrial internal standard glass thermometer, thermocouple thermometer, thermal resistance thermometer and pressure gauge thermometer. According to the principle of temperature measurement, the range of temperature measurement and whether it can be transmitted remotely, four kinds of thermometers are used in different temperature measuring occasions of air separation plant. Industrial internal standard glass thermometer is used in small air separation plant to measure the temperature of all levels of compressor gas and cooling water locally, and it is also used for temperature measurement during heating and thawing; thermocouple thermometer is used for purifier; thermal resistance thermometer is used for low temperature measurement inside cold insulation box; pressure gauge thermometer is used for measuring lubricating oil temperature.