The 1605 Qiongshan M 7 earthquake in Haikou, Hainan Province was the most destructive earthquake in the northern continental margin of the South China Sea. The earthquake caused massive subsidence and over 100 km2 of land sank into the sea in the coastal zone of the Dongzhai Harbor area. The earthquake epicenter and strong subsidence area is located in the Jiangdong New District (JND) of Haikou which are now in the planning and construction of Hainan Province. The systematic investigation of tectonic landform and composite drilling geological section revealed that the Maniao- Puqian fault (MPF) zone in the JND is composed of three north- dipping normal faults parallel to NEE i.e. the Maniao- Luodou fault (F2- 1), the Haixiu- Dongyuan fault (F2- 2) and the Changliu- Zhuxihe fault (F2- 3). The total length of the fault zone is about 132 km, which is complete or partially hidden. The overall performance is a normal fault, and the right lateral strike slip is the local segment. The length of the F2- 1 is ～132 km with vertical displacement ranging from 14. 8 m to 3. 4 m since Quaternary，the latest active age of the fault is about late Pleistocene. The length of the F2- 2 is more than 50 km with vertical displacement between 3. 3 m to 1. 8 m during the Holocene，the latest active age of the fault is Holocene. According to the seismic wedge and fault sag- pond accumulation, it is determined that the F2- 2, a branch fault of the MPF zone, is the seismogenic structure of the M 7 Qiongshan earthquake. The length of the F2- 3 is～58 km with vertical displacement of 112 m since Pliocene, the latest active age of the fault is between early and middle Pleistocene. The redefinition of the MPF zone structure, the latest active age of the fault and the determination of the seismogenic structure of the Qiongshan M 7〖SX(〗1〖〗2〖SX)〗 earthquake are of great significance for the planning and construction of JND of Haikou and the avoidance of active fault for general or particular structure and building in this area.