Much reference has been made to phenomenon that a generated screw thread flank may be re-cut by the outside corner of a milling cutter. But no precise analysis has been made on this phenomenon of the interference yet. This paper deals with a precise analysis of the interference involved in the screw thread cutting performed with a cone-shaped milling cutter. First, two kinds of interference which are involved in this cutting are clarified. Secondly, the methods of calculating the limit cutter pressure angles to avoid these interferences are given. Thirdly, the way to calculate the sectional shape of the generated screw thread is given. Fourthly, the correlations of interference to the cutter pressure angle, the lead angle of the screw thread, the cutter diameter are clarified by numerical examples. Finally, the theory is justified by the drawing of the sectional shape of the generated screw thread and the practical performance of the screw thread cutting and by the measurement of the sectional shape.