It is commonly used method to analyze the overall thermal characteristics of mechanical structure without considering the thermal contact resistance of components. But in terms of precision composite grinding machine, the impact of thermal contact resistance can not be ignored. On the basic of thermal contact resistance characteristics, this article gives the concept and empirical value of the equivalent area factor. By calculating the equivalent contact coefficient, the thermal contact resistance characteristics were integrated into the grinder simulation. According to the structure and processing characteristics of grinder, grinding machine was analyzed in two parts respectively to get the pattern of temperature rise and thermal deformation. Analysis shows the impact that thermal deformation has on working accuracy, so as to provide basis to the compensation of numerical control system to improve the working accuracy.