To analyze the lubricating state and the heating performances of the spindle bearings in ultra-high speed electric spindles, taken the characteristics of oil-air lubrication into account and based on the theories about rolling bearing dynamics and thermal elasto-hydrodynamic lubrication in point contact state, a model was built with the energy method for analyzing the heating performances the ball elements on both raceways in spindle bearings. An equation was derived for calculating the total quality of heat produced in a bearing. The influences of some basic factors such as the running speed, the axial preload, the oil viscidity, the design contact angle of bearing, and the ball materials and so on are analyzed on the heating performances in a bearing. The results show that it is easy to come into being elasto-hydrodynamic lubrication state for a bearing running in an ultra high-speed and lubricated by oil-air. It is also shown that the higher speed is, the more the quality of heat produced inside the oil films in the elasto-hydrodynamic lubrication state will be, which will bring the bearings working conditions worse.