In order to solve the problem that formation pressure changes after years of water injection development in henan oilfield, as well as the influence of formation heterogeneity and complex faults, the formation pressure becomes more complicated. Based on the seepage analysis formula and reservoir numerical simulation, the pressure relief radius of injection well and the distribution law of abnormal pressure in formation are studied, and the theoretical chart of pressure relief radius of injection well is established respectively. The two plates have little difference, but they have same trend and conclusion through verifying each other. The results show that the dimensionless pressure relief radius is greater than 0.5 when the underground injection-production ratio is greater than 1, and the dimensionless pressure relief radius gradually increases with the increase of dimensionless swept area. This chart not only provides a theoretical basis for the rational formulation of the field drilling and shut-in scheme in the high-pressure block of Henan oilfield, but also has a guiding significance for solving similar problems in other oilfields.