A coupled prediction model for temperature and pressure is developed for the annulus of multiple casings to prevent damaging the integrity of oil and gas wells due to annular pressures. The complex structure of the oil and gas well requires dividing the calculation of the annular pressure into three stages based on the annulus level. The annular temperature and pressure gradients of the wellbore are then studied. The hydrostatic pressure changes of the annular fluid at different temperatures, pressures, and well depths are analyzed considering the influence of the isobaric expansion coefficient and isothermal compression coefficient in annular fluids. The pressure gradients of annular fluids A, B, and C with production time and well depth are discussed along with the deformation of production casings. Results show that the annular fluid density and hydrostatic pressure decrease with the increase of temperature, while they will increase with the increase of annular pressure. The annular pressure increases first and then decreases from the bottom of the well to the wellhead. The annular pressure increases the fastest in the early production stages.