Cooling gas distribution ring is the core component of highspeed machine tool spindle bearing cooling. When measuring convective heat transfer coefficient of the oil mist on line, the spindle must be destroyed, the speed sensor is installed to obtain the speed of oil mist and then the data are gotten. A kind of nodamage calculation method based on fluid simulation Fluent was put forward to get the convective heat transfer coefficient of oil mist. It has vital significance on the thermal field analysis of motorized spindle research, also it provides a theoretical basis for similar problem. 