Abstract: During the exploitation of deepwater oil and gas wells, because of the particularity of the subsea wellhead, the thermal expansion of high temperature fluid in the wellbore causes the increase in annular trapping pressure, which leads to casing collapse and seriously threatens the wellbore integrity of oil and gas wells. Based on the law of constant volume thermodynamics and the mass balance principle in annular fluid, the influence of solid sedimentation of drilling fluid on the annular volume was considered, and a calculation model of multi-annular coupling trapping pressure in deepwater wells was proposed. The sedimentation laws and fluid thermophysical parameters of the commonly used drilling fluid systems were tested, and the influence of sedimentation time on the density, isothermal compression coefficient, and isobaric expansion coefficient of drilling fluid was obtained. By taking a gas production well in the South China Sea as an example, the annular trapping pressure of the wellbore was iteratively solved through the discrete grid method, and the factors affecting the annular trapping pressure were analyzed. The results show that solid sedimentation has a significant impact on the density of drilling fluid. With the increase in sedimentation time, the density of drilling fluid shows a significant downward trend. After 10 days of testing, the solid sedimentation of drilling fluid tends to stabilize. With the increase in sedimentation time, the variation range of the trapping pressure in annular space A is relatively small, while the increase range of the trapping pressure in annular space B and C is relatively large. The annular trapping pressure is positively correlated with the gas production volume, ground temperature gradient, Poisson’s ratio, and isobaric expansion coefficient and negatively correlated with the isothermal compression coefficient. The research results show that considering the influence of solid sedimentation can improve the accuracy of annular trapping pressure prediction, providing a theoretical basis for the selection of pipe strings and the design of production parameters in deepwater wells.