Abstract <p>The rheological performance of water-based composite salt drilling fluids under high-temperature and high-pressure (HTHP) conditions has been investigated. Using the composite salt drilling fluids from LH1 wells as the research object, its rheological parameters has been measured using a Chandler 7600 HTHP rheometer. The study compared the applicability of conventional rheological model for specific temperature and pressure conditions and explored the factor modification method for constructing HTHP rheological relations. The obtained results show that the temperature has a greater influence on the HTHP rheological properties of composite salt drilling fluid than the pressure. A conventional model fitting show that the three-parameter model outperforms the two-parameter one with the best result provided by the Herschel‒Bulkley (Herba) model, while the power-law model demonstrated the poorest result. This confirms the Herba model represents a HTHP kinetic rheological model for composite salt drilling fluids. By applying Arrhenius approximation, temperature factor corrections of the viscosity and the rheological model have been introduced to construct the coefficient functions of <i>n</i>, <i>K</i>, and <i>T</i> and establish the HTHP rheological kinetic equation. The revealed deviation anomalies are concentrated mainly at low shear rates (&lt;100 s^–1) and high temperatures (&gt;100°C), with residuals ranging from −4.464 to 0.581 and the average deviation of 3.16%. The studied analytical model demonstrates high predictive accuracy, which meets the field application requirements, and can be used for the rheological regulation of composite salt drilling fluids used for deep wells. This study provides a critical data support for optimizing the rheological properties of such fluids used in deep wells.</p>