Determining reasonable formation pressure plays an important role in improving oil recovery, reducing water consumption and casing loss rate. Whether the formation pressure is reasonable or not is also related to the stable production and economic benefits of the oilfield. For ultra⁃high water cut reservoirs, the study of formation pressure is relatively rare, and the existing methods do not take into account the influence of different viscosity, recovery degree and gas⁃oil ratio on reasonable formation pressure. Therefore, material balance method, gas⁃oil ratio dynamic data analysis method and numerical simulation method, are used to study the variation law of different viscosities, recovery degree, gas⁃oil ratio and formation pressure. Reasonable formation pressure values of each block are calculated, considering the influence of dissolved gas on crude oil viscosity and recovery factor, and the reasonable formation pressure values in the west part of central block of Daqing Oilfield are determined. The results show that the reasonable formation pressure in the west of the central region is close to the saturation pressure, the reasonable formation pressure in Sapu formation is 9.11 MPa, and the reasonable formation pressure in Gaotaizi formation is 10.12 MPa, which has important guiding significance for the later waterflooding development of Daqing Oilfield.