Abstract: Focusing on such problems as poor high-temperature stability of drilling fluids and downhole instruments in the development of deep gas and oil, phase change materials were introduced into drilling fluids for the first time to model the cooling of drilling fluids in deep wells based on phase change heat storage principle. First, the heat storage characteristics of the phase change materials were investigated on the basis of evaluating the thermophysical properties of the phase change materials. Then, the influence of phase change materials on the rheological and filtration properties of drilling fluids was comparatively evaluated. Finally, the experimental curves for the cooling performance of drilling fluids were measured using a self-made experimental device of drilling fluid circulating simulation. The results showed that the phase change temperature and the latent heat of phase change for the phase change materials 1^#–3^#were approximately 120–145 °C and 90.3–280.6 J/g, respectively; and the phase change material 2^# displayed the highest latent heat and the best heat storage performance of the phase change, exhibiting a compatibility withdrilling fluid. Specifically, the viscosity, shear force, and filtration of the drilling fluids were basically unchanged when the concentration of the phase change material 2^# increased to 12%, and the circulating temperature of the drilling fluids could be reduced by about 20 ℃, correspondingly. In addition, the phase change material 2^# exhibited excellent reuse properties. In conclusion, the circulating temperature of the drilling fluids could be reduced by referring to the principle of phase change heat storage of phase change materials, which could provide a new technical thinking to apply to cooling technologies for high-temperature drilling fluids in deep wells.