Abstract—The bearingless high speed motorized spindle (BHSMS) is a new type of spindle structure, which is driven by the torque winding of a modified motorized spindle and supported by a radial magnetic bearings, an axial magnetic bearings and the magnetic suspension winding of the modified motorized spindle. Without any contacting, BHSMS can reach extremely high speed when it rotates. Meantime, the temperature rise of BHSMS is also serious, because the electromagnetic loss of the motorized spindle and magnetic bearings produces a lot of heat during the process of rotation, which will affect machining stability. Therefore, in this paper, the heat sources and boundary conditions of BHSMS are analyzed and calculated. Then, a finite element model of BHSMS is established and its temperature field is simulated. The temperature distribution of BHSMS in the steady state is obtained. The interaction relationship among the internal heat sources is analyzed. It provides a theoretical basis for further study on the thermal performance of high speed motorized spindle.