Abstract: The design method of formed milling cutter for screw of oil extraction progressing cavity pump was presented.Through analysis on the shape of screw and the working principle of oil extraction progressing cavity pump,the spiral surface equation of screw was established.From the relative motion between formed milling cutter and screw,the profile equation of formed milling cutter which had constant back edge was established;it was based on the method of non-instantaneous envelope and the design principle of formed milling cutter.On this basis,the formed milling cutter of processing screw was designed.The formed milling cutter adopted method which the cutter head and the tool post was manufactured respectively,and it reduced the production cost and extended the service life of the milling cutter.The formed milling cutters designed by this method are applicable to processing screw of oil extraction cavity pump in common milling machine.The processing cost is reduced,and the machining accuracy and efficiency of screw is improved.