The invention discloses a temperature measuring device. The Temperature measuring device includes a sealed tube, an air pressure sensor and a controller; one end of the sealed tube end is connected with the air pressure sensor; the air pressure sensor is electrically connected with the controller; the controller comprises a central processor and a display device; and the sealed tube is filled with an inert gas. According to an ideal gas state equation pV=nRT, the specification and dimension of the sealed tube are set, and the filled inert gas is determined, and thereafter, parameters V, n and a constant R are obtained, and the temperature T of the gas is in direct proportion with air pressure p; the intensity of the pressure of the gas in the sealed tube is detected in real time through the air pressure sensor; the central processor calculates the current temperature T of the gas according to the equation and the parameters; a temperature numerical value is displayed on the display device; and temperature measurement can be completed.