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.