The Sangshandao gold deposit belt is located in the western metallogenic area to northwest of the Jiaodong gold deposit cluster district, which is the most important gold base in China. Recent years has witnessed great breakthrough in ore prospecting in concealed areas such as deep earth and waters. As an important orehosting structure, the positions of extension of the Sanshandao fault into the waters have not been determined. In order to find out the extended positions of the Sanshandao fault belt in the north and south ends into the waters, this study carried out marine largescale gravity measurement using INO seafloor gravimeter. In the Bouguer gravity anomaly map, the Sanshandao fault is characterized by a largescale gravity gradient belt with various gravity changes, which presents an “S” shape in the plane. The Sanshandao fault extends northward into the sea across the Sanshandao gold mine, and southward cross Xinli to the Bohai Sea and then passes through Cangshang and Panjiawuzi eastward to the Bohai Sea. Combined geological features of the gold metallgenic belt, the northeastern extension position of the Sanshandao fault was inferred using gravity anomaly data and confirmed through drilling deployment. The main lithology of the core is fine grained monzonitic granite (including biotite), monzonitic granite, cataclastic granite, beresitization granite. Dark dykes are dominated by gabbro, with minor amount of biotite diorite and diorite porphyrite. The biotite minerals show directional arrangement and dykes underwent varying degrees of alteration. Tectonic alteration (mineralization) zone has a width of 20625 meter （87659m~108284m）. The alteration zone has obvious boundary with hanging wall rock and gradually changing alteration boundary with footwall rock. Seven layers of orebodies have been delineated, with an accumulated thickness of orebodies reaching to 283m and the largest apparent thickness of 1606 m for a single layer of orebody. Drilling positions are located within the noseshaped area of gravity gradient variation, and the spatial position is in accordance with the distribution law of the distance distribution, the corresponding output, distribution law of the segmented enrichment and so on. Drilling cores contain polymetallic sulfide mineralization, such as chalcopyrite, gelana, and pyrite, which shows the features of typical deposit cluster area. Therefore, it is concluded in this study that this area should be another target area with large prospecting potential after discovery of the 470ton superlarge gold ore deposit in the offshore of the northern Sangsandao fault.