Abstract: The thermal deformation of the motorized spindle is one of the main factors affecting machining accuracy, and the thermal deformation is mainly caused by the temperature rise of the motorized spindle. The cooling system is the key factor affecting the temperature rise of the motorized spindle. In order to optimize the key technical parameters of the cooling system, taking a certain type of high-speed motorized spindle as an example, a thermal characteristic modeling is established by considering the heat transfer coefficient of different rotating surfaces of the spindle. The simulation accuracy of temperature field and thermal error is improved. The correctness of the simulation model is verified by the temperature rise and thermal error experiments at different spindle speeds. Based on the established simulation model of the thermal characteristics of the motorized spindle, the cooling system parameters were optimized by using the orthogonal test. After optimizing the cooling parameters, the simulation experiment results show that the maximum temperature of the motorized spindle is reduced by 2.0 ℃, and the thermal deformation is reduced by 25.76 μm, which provides a theoretical reference for optimizing the cooling system of the motorized spindle.