Abstract: The disclosure includes a temperature measuring device and a temperature measuring method for measuring the temperature of molten metals. The temperature measuring device includes a temperature sensing element, a support tube, a connecting tube and an exhaust structure. The temperature sensing element is a cermet tube with a closed end and an open end, and can sense the temperature of a molten metal and emit stable thermal radiation energy based on the blackbody cavity principle when being extended into the molten metal. The open end of the cermet tube is fixedly connected to one end of the support tube, the cermet tube is communicated with the support tube, and the other end of the support tube is fixedly connected with the connecting tube. The exhaust structure is used to discharge the smoke inside the cermet tube and the support tube.