Abstract: The average reservoir burial depth of extra low permeability oil reservoirs in X Oilfield is 2 300 m and their average permeability is only 2.1 mD.And in the process of development, the single-well daily water injection is lower than 15 m³ in most fault blocks and the oil production rate is lower than 0.3%.Thus, the large-scale produciton increase of extral low permeability oil reservoirs is restricted seriously.In this paper, the large-scale fracturing technology was introduced to realize the effective water flooding development of extral low permeability oil reservoirs.After the main mechanisms of increasing single-well production rate and decreasing injection/production well spacing by large-scale fracturing were investigated, the dynamic simulation of postfrac water flooding was estabished.It is confirmed that large-scale fracturing wells have the following water flooding development characteristics, i.e., high production rate in the early stage, fast water flooding response and fast rising of water cut after the response.In view of these characteristics of postfrac water flooding development, it was proposed to adopt the fracturing mode of "different layers in neighboring wells and the same layer in interval wells" and implement the water flooding energy implement method which combines postfrac pressure boosting with cyclic water flooding.It is indicated that the single-well production rate after the application of large-scale fracturing techlogy is 200% that of conventional fracturing, the water flooding recovery factor is increased to 26% based on the optimization of fracturing design and water flooding energy supplement mode, and thus extra low permeability oil reservoires can be developed effectively by means of water flooding.