Abstract: To accurately grasp the distribution characteristics of annulus temperature and pressure in variable pressure gradients drilling, based on the theory of flow and heat transfer of wellbore fluid while fully considering the heat and mass transfer of the fluid with variable mass at the position of separator and the change of the physical parameters of circulating fluid with temperature and pressure, the paper establishes a model for predicting the annulus temperature and pressure in variable pressure gradients drilling, uses a double-cycle iterative algorithm to solve the model, and carries out a study of numerical simulation for the distribution of annulus temperature and pressure. The results show that compared with conventional drilling, there is an obvious inflection point on the distribution curves of annulus temperature and pressure in variable pressure gradients drilling, and the position of the inflection point is consistent with that of the separator; due to the injection of the hollow spheres with low thermal conductivity, the annular fluid temperature in in variable pressure gradients drilling is lower than that in conventional drilling; the position and efficiency of separator, density and volume fraction of the injected hollow spheres have great impacts on the distribution of annulus pressure in variable pressure gradients drilling.