In order to research on the spindle thermal stability by water cooling system of the high-speed motorized spindle,the cooling effects of cooling system of the high-speed motorized spindle by using orthogonal test method under different working conditions were researched.The heating power of motorized spindle and orthogonal test of coolant velocity were designed.The heating power was divided into three levels,and the coolant velocity were taken separately as 0.3,0.4,0.5,0.6,0.7,0.8 m/s,then the experimental results of motorized spindle under every working conditions were gotten based on the Compute Flow Dynamics software(CFX)simulation test.The results of orthogonal test show that the temperature of spindle can only be reduced for 5~8 ℃ by adjusting the coolant velocity under every working conditions and the optimal working temperature of spindle is at 40 ℃.The method of orthogonal test provides the numerical basis for accurate temperature control of motorized spindle.