Thread whirling process is a cutting process in which a series of cutting edges on the whirling ring remove material by turning over the rotating workpiece. Whirling unit attached to a thread whirling machine influences much on the machining accuracy because the main sources of heat generation are assumed as bearings, servo motor and chip formation during machining. Analysis of temperature distribution, thermal deformation and thermal stress of the whirling unit has been carried out. It is revealed that the highest temperature of 91°C reaches in the bearing and relative displacement from point A to tool reaches 0.02~0.03mm along X, Y and Z axis. The maximum thermal stress of 31.9MPa is developed in the unit.