Two-stage UCG is an effective technique to produce water gas with high heating value; its gas producing process is mainly determined by temperature. On the basis of the model experiment, via the analysis of the temperature field distribution regularity in the gasified coal layers in the gasifier and the generalization and treatment of the boundary conditions, two-dimension nonlinear unstable mathematical models of the temperature field in the two-stage UCG are established, and the method of selecting model parameters is illustrated. Solution is made through the method of volume controlling. This article also analyzes the results of calculation. In the light of the numerical computation results, the calculation value of the temperature field for coal seams of combustion and gasification can better fit with the experimental one under the condition of the model experiment. Except for some measuring points in the vicinity of the flame working face, where the relative error between computation value and test value is comparatively high, those of other measuring points are all below 15%, which completely meets the accuracy requirements for the numerical simulation on the temperature field of UCG. The consistency between the calculation value and the measurement value indicates that the numerical simulation of dynamic temperature field of coal media in the gasifier is correct, which provides necessary theoretical basis for further quantitative study of the UCG process.