Abstract: The fractured-vuggy carbonate reservoirs in Tahe oilfield are characterized by special reservoir types and difficult exploitation. The previous single well water injection and element pattern water flooding obtained better oil incremental effects to some extent. However, the development effect was getting poor with the continuous water flooding for the plentiful oil that water flooding can’t sweep was remained in high parts of fractured-vuggy units. This paper studied and proved the possibility of nitrogen huff and puff process for the remained oil by means of numerical simulation technique. When injecting nitrogen gas into the formation, it will mix up with the crude oil and appear gravitational segregation to replace downward and produce the oil, also, the injected nitrogen dissolved in the remained oil can play a role of reducing the oil viscosity and complementing the formation energy or pressure. This technology has been applied to 123 wells in Ordovician fracture-vuggy carbonate reservoirs in Tahe oilfield since 2012, and the cumulative oil production amounted to 16.13×104 t. It is verified that it is a feasible EOR technology for such a reservoir