The rheological parameters of drilling fluid have an important impact on accurately predicting the hydraulic parameters of deepwater and ultra-deepwater drilling wells. The rheological experiments were carried out on commonly used HEM (high efficient mud) drilling fluids and synthetic-based drilling fluids in the deep waters of the South China Sea under conditions of 4 to 210 ℃ and 30 to 180 MPa. The variation laws of rheological parameters such as apparent viscosity, plastic viscosity, and dynamic shear stress with temperature and pressure were revealed in a wide range of temperature and pressure. Based on the experimental data, nine existing rheological models were compared and evaluated. It was found that the Ross model is suitable for synthetic-based drilling fluid, and the Herschel-Bulkley model is suitable for HEM drilling fluid. On this basis, a general predictive model for rheological parameters of HEM and synthetic-based drilling fluids was created, which is applicable to alternating high and low temperatures, high and low pressures. The maximum error of this model is 11.95%, with an average error of 0.62%, which is better than existing models. The bottom hole pressure error is 0.28% when using HEM drilling fluid and 0.181% when using synthetic drilling fluid, which can meet the requirement of deep water drilling in the South China Sea.