Carbonate reservoir space is mainly fracture or dissolution cave in Nanpu offshore，Bohai Bay basin，the formation of which is controlled mainly by paleo-karst. The paleo-karstification and models of paleo-karst for the target stratigraphy were characterized in detail based on core description，mud-logging，imaging logging and outcrop investigation. The lithology of the Cambrian-Ordovician carbonate reservoir in buried hills consists of micritic limestone，argillaceous micritic limestone，grainy pelsparites and mudy pelsparites. Based on core descriptions，there are calcareous sandstones and conglomerates，calcareous breccias，bauxitic mudstones and collapse breccias formed by paleo-karstification. Logging shows large quantities of mud losses and nothing is drilled. The FMI loggings show large amounts of pores，caves and fractures generated by dissolution during paleo-karstification. Outcrop investigations show that a paleo-karst system can develop in the target interval of the Ordovician stratigraphy. These evidences manifest that the paleo-karstification occurred in the buried hills of Nanpu offshore，and the development of a large amount of vertical and horizontal caves indicates the formation of vadose zone and phreatic zone respectively. Faults and fault-associated fractures play positive role in paleo-karstification. A model of the buried-hill paleo-karst was established based on the model of outcrop karst and the characteristics of the buried-hill paleo-karst，which can visualize the distribution of the buried-hill reservoirs and have directive significance to the further petroleum development.