Abstract: Thermal conductivity is the decisive factor in the accuracy analysis of thermal deformation, which is one of the key reasons affecting the precision of ultra-precision machine. In order to ensure the accuracy of temperature field distribution analysis and improve the machine precision, a thermal conductivity analysis model based on thermodynamic theory and a structure optimization method of machine tools through the finite element analysis are presented. To improve the analysis accuracy of the thermal conductivity, free electron gas model and Debye model are applied to calculate the thermal conductivity of main materials of ultra-precision optical machine tools. The temperature field distribution of spindle, carriage and bed can be obtained through the finite element analysis software such as ANSYS. Based on the study of temperature rise law of the spindle and the complete machine, a structure optimization method of ultra-precision optical machine is finally presented in the error sensitive direction by reducing the contact area between the motor，spindle and carriage, optimizing the connections between the motor，spindle and carriage. As a result, the thermal deformation is reduced and the machine accuracy is improved.

Key words: structure optimization, temperature field distribution, thermal conductivity, ultra-precision optical machine