<p>To better predict the cutting temperature during 3D ultrasonic vibration–assisted turning, this paper establishes a mathematical model for calculating cutting heat based on the classical theory of heat distribution, and the heat dissipation in the discontinuous cutting process is considered. The accuracy of the model was finally calibrated experimentally. The effects of turning speed, depth of cut, feed rate, and amplitude of the tool nose on cutting temperature were analyzed. The results indicate that turning speed significantly affects the cutting temperature, and the amplitude of the tool nose has the slightest effect on cutting temperature. In the range of lower turning speed, the heat source of the shear plane plays a dominant role in workpiece temperature; in the range of higher turning speed, the heat source motion and heat distribution coefficients play a dominant role.</p>