To safeguard the stability of deep-sea wells under high temperature and pressure, and to avert the hazard of substantial alterations in the drilling fluid's volume that could be triggered by temperature shifts, which may lead to the risk of annular pressure, accurate prediction of the thermal expansion coefficient of the drilling fluid was a key factor in assessing and controlling the annular pressure. Therefore, through the experiments on the PVT characteristics of drilling fluids, the coefficients of the drilling fluid's thermal expansion were fitted to the corresponding temperature-pressure ranges, a corresponding predictive model was constructed and confirmed, utilizing the formula for fitting. Drawing on the fitting formula, a corresponding prediction model based on the measured thermal expansion pressure of drilling fluid was established and verified to form a set of prediction methods for the thermal expansion pressure of deep water high-temperature and high-pressure gas wells based on the measured circumferential pressure. The results show that the annulus temperature at the subsea wellhead decreases in the late production period, however, it exceeds the temperature at the mudline, resulting in an escalation of the thermal expansion pressure. The fluid pressure within the tubing diminishes as production progresses, increasing the risk of tubing column failure. Based on the drilling fluid PVT characterization experiments, the fluid thermal expansion coefficient was predicted and found to vary significantly with production and formation pressure, with a reduction rate of up to 38.9%. Drilling fluid Ⅱ performs better in controlling the thermal expansion pressure in the annulus and is recommended for managing annulus pressure.