The South China Sea and its adjacent areas are located at the southeast end of the convergence zone of Eurasia and Gondwana, which is an important area where the Tethys tectonic domain meets the Pacific tectonic domain. The Tethys suture zone enters the South China Sea along the Jinshajiang-Ailaoshan structural belt, which suggests that there may be Tethys ocean traces in the South China Sea and that the suture zone exists in the magnetostatic area. Based on the interpretation results of geophysical data on the northern continental slope of the South China Sea, including gravity, magnetic, submarine seismic and deep reflection seismic data, as well as the analyses of regional geological characteristics, this paper studies the genesis of the high magnetic anomaly zone and magnetostatic area in the northern continental margin of the South China Sea. It is considered that the high magnetic anomaly zone is a continental margin volcanic arc formed by the turning and subduction of the Paleo Pacific Plate in the Middle Cretaceous. The magnetostatic area experienced the late continental margin rifting and the opening of the Paleo-South China Sea and South China Sea, and experienced the bottom splitting of high-temperature thermal materials, which caused the crustal tension and thinning, and the Curie uplift to form the magnetostatic area. After the expansion of the South China Sea, the original subduction zone may have migrated to the south of the South China Sea or subducted and disappeared, and there is no suture zone.