To meet the temperature measurement requirements in a confined high-temperature environment, a longitudinal mode ultrasonic guided wave temperature measurement method based on a high-purity graphite rod is proposed. By considering the temperature-dependent dispersion equation, the main factors affecting the wave velocity due to temperature are analyzed, and suitable excitation frequency and modes for temperature measurement are selected. A prediction model for the variation in the guided wave signal transit time with temperature in a waveguide rod with non-uniform temperature distribution is established, allowing for the calculation of accurate echo transit times in the graphite rod. Temperature measurement experiments using guided waves within the range of 1000℃ were conducted to verify the model’ s accuracy. The experimental results demonstrate that the temperature measurement accuracy of L(0,1) mode guided waves with an excitation frequency of 30 kHz is within 10℃ , with good repeatability across multiple trials. The research in this paper proves the high-temperature measurement capability of ultrasonic guided wave, providing a feasible solution for temperature measurement in extrem high-temperature environments.