Abstract： Aimed at the problem that the manual wall thickness acquisition algorithm has the disadvantages of large labor intensity, low efficiency, and so on, and the fact that the existing automatic wall thickness acquisition algorithm is not accurate and adaptable, the automatic wall thickness acquisition algorithm based on the improved secondary 1.5-D spectrum estimation was proposed. The pipeline ultrasonic A-wave signals were estimated by 1.5-D spectrum that were intercepted and filled zero by the upper and lower limit of the wall thickness. Then, the 1.5-D spectrum estimation was done again, and the wall thickness information was obtained. Experimental results show that  the wall thickness data generated by this algorithm is more accurate and the relative error is within 3%.