On account of the high-speed motorized spindle system,the heat generated will inevitably produce a fever and lead to the spindle thermal deformation. In this paper,the thermal characteristics of high speed spindle unit were analyzed based on the ANSYS. This text uses the finite element method for modeling to calculate the heat generated and the thermal convection on each part of the spindle;through the analysis of ANSYS,the temperature distribution of high-speed electric spindle unit,axial and radial displacement at the end of main spindle and corresponding displacement diagrams are obtained. The thermal state performance can be analyzed thermal induction pre load,and calculated the homologous intensity and the critical speed. The study also found that the effect of heat induced pre load should be considered in order to obtain more pre load.