A vertical thermal diffusivity measuring device based on laser flash method is introduced. The device uses pulsed laser to uniformly heat the sample, which generates one-dimensional heat flow inside the sample. The temperature rise signal of the sample is measured by infrared detector. The temperature environment is measured by vertical vacuum heating furnace, and the thermal diffusivity is measured from room temperature to 1600 °C. A stainless steel sample with a thickness of 1.1 mm and a diameter of 10 mm is measured using this device. The deviation between the measurement results and PTB reference data is less than 1%.