The rheological parameters of drilling fluid play an important role in safe drilling and preventing overflow and leakage, but it is greatly affected by temperature and pressure, and it is difficult to characterize the rheology of drilling fluid with large temperature and pressure span. Therefore, in this paper, the rheological experiments of the two systems of drilling fluids commonly used in the Bohai Bay Oilfield under the conditions of large temperature and pressure span (4–200 °C, 30–150 MPa) were carried out, and the variation of rheological parameters such as apparent viscosity, plastic viscosity, dynamic shear force, fluidity index and consistency coefficient of the two systems with different temperature and pressure conditions was revealed, and then the applicability of the nine commonly used rheological modes of large temperature and pressure span to the drilling fluids of the two systems was evaluated, and it was found that the R-S mode was suitable for the drilling fluid of the 1# system and the power law mode was suitable for 2#drilling fluid. It can provide a theoretical basis for the optimization of hydraulic parameters in field drilling operations.