Abstract: This paper introduces a new kind of three dimensional,two phase(oil and water) numerical simulation model of reservoir and fracture by employing the coupling reservoir-fracture method.Numerical simulation can be carried out on the result of production well fracturing in different well patterns based on the methods of rectangle grid subdivision for fractures and PEBI grid subdivision in the reservoir joint.The paper gives an example in Shishen 100 fault block pools of low permeability in Shengli Oilfield.Under the condition of inverted nine spot well patterns,the comprehensive effect evaluation indexes are proposed to conduct optimizing calculation for fractured injection well design.The results supply a research method for the fracturing design and effect evaluation of the injection wells in low permeability reservoirs and are important for improving the water-flood effect of low permeability oilfield.