The stainless steel 1Cr18Ni9Ti’s toughness is very large ,it is difficult to cut, especially the bad rigidity of long trapeziform double-edged inner screw thread which arose libration and ripple when cut . By connectting the slip oriented pole and cutter pole the latter’s rigidity is promoted ,in order to decrease the finish machining’s surplus ,the machining of screw thread is divided to three step: slotting, preforming and finish machining.The effect is prominent by controlling the cutter’s shape, dimension and geometrical angle , at the same time considering the influence of screw thread’s rising angle .