Abstract: In the field of pipe wall thickness corrosion monitoring, piezoelectric ultrasonic technology plays an important role. When the pipe wall thickness is measured by piezoelectric ultrasound, the change of pipe temperature will affect the performance of the ultrasonic coupling agent and lead to the change of the amplitude of the reflected wave, which makes the ultrasonic time-of-flight cannot be calculated correctly by the threshold method and the envelope analysis method, resulting in large wall thickness measurement errors. To solve this problem, a piezoelectric ultrasonic wall thickness measurement system for variable temperature pipeline was built in this paper. Ultrasonic time-of-flight measurement method based on correlation analysis was used to calculate ultrasonic time-of-flight, and the ultrasonic wave velocity was compensated by temperature and wave velocity correction model, so as to improve the measurement accuracy of variable temperature pipeline wall thickness. The results showed that the resolution of pipe wall thickness measurement was increased to 0.01mm, and the measurement error of pipe wall thickness was less than 0.05 mm, and the proposed measurement method could realize the measurement of pipe wall thickness at temperature ranging from －20 ℃ to 70 ℃ and meet the requirements of piezoelectric ultrasonic temperature variable pipe wall thickness monitoring.