At present, multiwell and multilayer conditions have been adopted for most oilfields. In this article, a formation pressure calculation model is established for multiwell, multilayer, variable production and unstable seepage oilfields. An example of the drilling and shut-in area in eastern North Block 3 is calculated. Based on the actual parameters of the basic well pattern in the drilling and shut-in area, a physical model of formation pressure variation is established. When the physical properties of vertical reservoirs are quite different, the liquid-producing capacity of each layer is divided according to the Kh value of each layer. Combined with the principle of pressure superposition, the suitable definite solution conditions are given. A mathematical model for calculating formation pressure with multiwell and multilayer variable flow rate is established. Using the ratio X1: X2: X3: X4: X5 = 2:3:4:5:6, giving the permeability of each layer, and a schematic diagram of the formation pressure distribution field a mathematical model is constructed. Six different drilling points are selected and the formation pressure is calculated when the composite water cut reaches 96%. The results show that the pressure of the high-permeability layer is low and the pressure of the low-permeability layer is high. It can be seen that the plane formation pressure distribution of the mathematical model presents a regular distribution pattern of a dumbbell–spindle type. In the longitudinal direction, the positive rhythm oil layer presents a scheme in which the formation pressure gradually decreases.