Abstract: The oceanic core complex(OCC)is a new style of sea floor structure discovered in recent years. OCCs are mainly found on both sides of the slow and ultra-slow spreading ridges. Recent study of OCCs is mainly carried out on the Mid-Atlantic Ridge, Southwest Indian Ridge, Central Indian Ridge and Southeast Indian Ridge. Surface corrugations and lineations are the main features for identification of OCCs, and detachment fault parallel to ridge axis, rift valleys and normal faults on the hanging wall are all the important structures of OCC systems. Serpentinite gabbro, olivinite and the thin oceanic sediments compose OCC. The development of OCCs has much link with ocean ridge spreading velocity, manga supply and detachment fault:the manga supply at slow and ultra-slow spreading ridges is not enough to balance the ridge spreading-caused strain vacancies. There needs detachment fault on the weak zone to bring the rocks from mantle to the sea floor for balance. The development of OCCs experiences four stages including embryonic stage, development stage, maturity stage and decline stage. OCCs maybe the favorable structural setting for hydrothermal sulfide and a new off-axis hydrothermal system to provide substance, heat resource and favorable passages for the hydrothermal system and mineralization.