Accurate size information measurement of the sealing components of proton exchange membrane fuel cell stacks is essential for preventing the escape of reactive gases from the cell reaction zone. Consequently, this study proposes a three-dimensional (3D) reconstruction method for flexible thin-walled parts based on a laser point cloud. By designing groove calibration objects and nonchamfered measuring blocks, the calibration object features are extracted from the contour data collected by each line laser contour sensor. Subsequently, the relative positional relationship of these features is used to accurately calibrate the optical plane and linear guide motion direction. We set overlapping areas and employ an improved point-to-surface iterative nearest point algorithm to fuse the point cloud data during the motion process of a single sensor. Combined with the calibration object characteristics, the transformation relationship between the different sensor optical plane coordinate systems is calculated by employing the principal component analysis method and consequently constructing the covariance matrix. The results demonstrate that the standard deviation of the system measurement results is approximately 0.01 mm. Furthermore, the proposed method accurately measures the 3D morphology and thickness information of flexible thin-walled test objects, and the measurement efficiency and accuracy satisfy the requirements of proton exchange membrane fuel cell stack seals in the industry.