Abstract: Aiming at the limitations of two-dimensional images in three-dimensional characterization of defects in the lead seals of high-voltage cable terminations, this paper proposes a three-dimensional imaging inspection method for lead seal defects based on a one-dimensional phased array. The method acquires three-dimensional point cloud data of the lead seal surface using laser scanning, plans the inspection path by integrating NURBS curve fitting with an equal-arc-length discretization algorithm, and designs a coupling device to address acoustic beam coupling challenges on complex curved surfaces. Sequential B-scan images are preprocessed using adaptive geometric masking and feature extraction algorithms, and final three-dimensional reconstruction is achieved via volume rendering. Results show that: (1) the 3D imaging clearly characterizes the spatial distribution and columnar morphology of defects; (2) the absolute error in defect depth ranges from −0.6 mm to −0.2 mm, with a relative error of −6% to −1.3%; (3) the maximum relative error in through-hole depth is approximately ±8%; and (4) the relative error in volumetric quantification satisfies the accuracy requirements for industrial inspection. This method enables 3D morphological reconstruction and quantitative evaluation of internal defects in lead seals, thereby providing technical support for full-lifecycle management of high-voltage cable terminations.