Abstract: Oceanic core complex, a new structural type, was proposed to explain many listric detachment faults and ridge-perpendicular lineations such as megamullion in the Atlantic by comparison with the metamorphic core complex in the continent. The oceanic core complex consists of three parts based on deep seismic reflection profile. The first part is dominated by brittle deformation in layer 1 and layer 2 of the oceanic crust. The second part is brittle-ductile transition layer dominating the detachment fault. The detachment fault zone is composed of white carbonite, strongly serpentinized peridotite or basalt, ultramafic mylonite and mylonitic gabbro and others, rather than felsic mylonite and chlorinized breccia. The detachment surface is covered with thin, unmetamorphic and oceanic sediments, or directly crops out on oceanic crust. Under the detachment fault is retrograde metamorphic hot oceanic mantle. The third part is the core of oceanic core complex, which is dominated by ductile deformation intruded structurally by diapiric ultramafic plutons, especially gabbro intrusions. The oceanic core complex of the oceanic crust is obviously different from the metamorphic core complex of the continent. The oceanic core complex can result in a displacement of several kilometers along the detachment fault, producing local offsets of seafloor magnetic zones and the complexity of structural pattern in the oceanic crust.