Simulation analysis of thermal deformation of machine tool is the base of thermal balance design and thermal error compensation.In order to improve the accuracy of the thermal deformation simulation, through optimizing calculation method of heat and reasonably designing analysis process, ANSYS Workbench thermal simulation analysis and temperature test of ultra hard turning CNC lathe hydrostatic spindle system were made. The results indicate the error is within 5%, to ensure the validity of the thermal deformation simulation; the deformation simulation shows the maximum deformation of the front spindle and on the three directions is 5 μm.It provides a theoretical basis for the thermal error compensation. The temperature changing curve of each heat source at the same speed was obtained. It provides a theoretical basis for improving the machining precision through reasonable preheating.