The Fushan Sag is a secondary tectonic unit in the southeastern coast of the Beibuwan Basin which is located in the northwestern of the South China Sea. Based on the interpretation of the 3D seismic data and the contrast of tectonic characteristics between the western and eastern area, a transfer zone is found in the centre of the sag. The transfer zone was mainly developed in the Palaeogene Liushagang Formation and located above the Huachang low uplift at the intersection of the western and eastern areas. Two extensional structure systems were developed respectively at two lateral sides of the transfer zone. There were significant differences on the strike of faults and structure styles between the two systems. The formation of the transfer zone was caused by the existence of strike-slip process with the development of flower structure. The transfer zone is the entrance of source and controls the distribution of sand and deposition system through the counseling function of regulation faults. The deep antithetic fault system is favorable to form various kinds of traps and control the most petroleum accumulation distribution. The complex structure system contributes to the formation of the fault block reservoir and fault-nose pool and improves the quality of sandstone reservoir. The transfer zone holds distinct hydrocarbon accumulation with two oil resources and various types of reservoir. In all, the transfer zone has a good control effect on hydrocarbon accumulation and has good prospects for hydrocarbon exploration.%基于典型三维地震解释结果,结合东西部构造差异特征,在福山凹陷中部识别出一个构造转换带,该构造转换带主要发育于古近纪流沙港组沉积时期,位于东西部接壤部位花场低凸起之上,转换带两侧分属为2个伸展构造体系,断层的走向和构造样式具有较大的差异性.花状构造的发育表明存在区域走滑作用,与转换带的成因密切相关.构造转换带为物源入口,控制着砂体和沉积体系的运移方向和展布范围；深层反向断裂有利于油气的疏导和封存；复杂的断裂体系有利于断鼻和断块圈闭形成,同时有利于改善储层物性.构造转换带具有双向油源条件,发育独特的油气成藏模式和多种油气藏类型,由此可见该转换带对油气成藏具有良好的控制作用,具有良好的油气勘探前景.
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