A large amount of heat is generated during the working process of high-speed motorized spindle, which leads to thermal deformation of the front end of the spindle. The machining accuracy of the spindle is affected seriously. In this study, the thermal error prediction model of the motorized spindle with variable load preload is proposed. The heat transfer theory calculation and the bond diagram model are combined. In this way, the thermal elongation of the motorized spindle with similar structure can be predicted accurately in real time. The thermal-solid coupling model of the spindle is formulated, and the distribution of temperature field of the spindle under coupling action is achieved by the finite element analysis. According to the distribution law of temperature field and the flow direction of heat energy, the integral model of the spindle is divided into nodes by the thermodynamic theory. The thermal parameters of the nodes are calculated. The 20-sim platform is used to establish the thermal bond diagram model of the spindle, and the real-time temperature monitoring module of the key nodes is associated with the thermal elongation module. According to the thermal elongation of the nose end, the thermal deformation of each key point is calculated and the thermal error modeling is completed. Experimental results show that the prediction model error of the formulated bond graph is within 0. 5 μm. Research results can provide a theoretical basis for real-time thermal error compensation of intelligent motorized spindle under different working conditions.