Abstract: The feasibility and effectiveness of the detection scheme are critical issues determining operational success rates and efficiency. To address these challenges during scheme design, establishing a theoretical model for underwater target magnetic anomaly and applying forward modeling to simulate target detectability and magnetic anomaly characteristics represents the preferred methodology. Using Poisson's Equation for gravity and magnetic potential fields, we derived a model for calculating the total-field magnetic anomaly of an underwater point source target, ignoring remanence. Simulation analyses quantified how key parameters influence magnetic anomaly characteristics. Building on this foundation, we established a framework for predicting underwater target magnetic detectability. This framework requires predicting a target's magnetic anomaly characteristics using known target parameters, ambient geomagnetic field conditions, and water depth. We further propose an optimized magnetic survey line design that balances detectability constraints with operational challenges in observation plane control (specifically magnetometer towfish altitude). We classify magnetic detectability of underwater point source targets into four levels based on anomaly amplitude: undetectable (0–3 nT), weak (3–10 nT), medium (10–50 nT), and strong (＞ 50 nT). Crucially, aside from objective factors, observation altitude (R) represents a major operator-adjustable parameter governing detectability. For magnetic surveys targeting underwater point sources, a grid-like layout is optimal. The main survey lines should be oriented at D. Optimal line spacing equals one-third the width of the magnetic anomaly zone perpendicular to the main survey direction. To precisely locate targets on magnetic anomaly contour maps or main profiles, we define a positioning quantile (P_fra). This parameter exhibits an inverse correlation solely with geomagnetic inclination (I), for which we provide a fitting formula. P_fra can be calculated from the survey area's geographic coordinates, enabling rapid target localization during over-water detection.