Abstract <p>Electrical resistivity tomography (ERT) is a widely used method in geological exploration and plays a significant role in engineering applications. However, its application in marine surveys has been limited due to equipment and methodological constraints. While some studies have demonstrated promising results using 2D methods in engineering, the more geologically accurate 3D methods have seen limited practical application due to challenges such as low data acquisition efficiency, high computational costs, and strong inversion non-uniqueness. To address these challenges in nearshore marine environments, we propose a 3D resistivity detection and interpretation method tailored for stratigraphic division. A typical layered seafloor model was constructed, and the resistivity imaging response of marine strata was investigated using a four-electrode observation system with parallel survey lines on the seabed. Based on this, an anisotropic inequality-constrained inversion method was developed to generate resistivity cross-section images, which were interpreted in conjunction with existing borehole data. This approach successfully achieved accurate stratigraphic division at the test site, validating the effectiveness and feasibility of the proposed method.</p>