With the rapid development of horizontal well technology and the theory of low permeability reservoir exploration, applying the horizontal well to explore low permeability reservoir is an important measure for improving the recovery efficiency of the low permeability reservoir. However, in the previous research, horizontal well is regarded as the production well. Thus the research on the horizontal well as an injection well is rare. Consequently, the water injection technology of the horizontal well provides a new idea for the reasonable exploration of the low permeability reservoir. Considering the current research situation, a 3-D model about the injection capacity evaluation of selective perforation horizontal well is established based on the principle of superposition. The relationship between equivalent radius and perforation length as well as the location of the horizontal well is analyzed; the distribution of the flow and pressure for the horizontal well is discussed based on the established model. All the foregoing theoretical research is applied to the Yushulin Block of Daqing Oilfield and the result indicates that due to its accuracy and reliability, the established model has the important significance of guidance and popularization value for the horizontal well injection exploration of the low permeability reservoir.