Abstract: This paper proposed a new ultrasonic thickness measurement technology with self-calibration function which could effectively eliminate the influence of temperature variation on sound velocity so that it could on-line monitor the corrosion condition of metal pipeline of oil and gas. In this paper, the fast Fourier transform (FFT) was used to filter out the interference clutter in the self-calibration ultrasonic wave, and then multi-extrema of the echo signal were selected to calculate the thickness of the measured object. It is proven that the self-calibration ultrasonic thickness measurement technology in this paper has good detection precision and stability.