Advancements in 3D CAD allow product shape to act as a common language to represent and retrieve reusable product information in PLM systems. While shape-based retrieval techniques contribute to the part design reuse process by retrieving similar part models, selecting the optimal candidate for reuse remains a challenge. A more refined shape comparison process is required to locate single shape differences between reference and candidate CAD models, and to represent them intuitively and functionally in relation to part design. We have developed a 3D CAD model comparison method focused on the representation of shape differences between similar models with respect to the reference’s geometric constraints. The proposed method comprises the explicit representation of CAD data, the mapping and differentiation of B-Rep model elements and the re-evaluation of geometric constraints according to shape differences. It will contribute to reliable decision making by promoting part design reuse during the development of new mechanical products.