Through　analyzing　the　shape　of　screw　of　oil　extraction　progressing　cavity　pump,　a　spiral　surface　equation　of　the　screw　was　established;　and　from　the　relative　motion　between　formed　milling　cutter　and　screw,　the　basic　profile　equation　of　formed　milling　cutter　was　established　with　molding　milling　principles　and　coordinate　transformation　theory.　According　to　the　actual　use　of　milling　cutter,　aimed　at　the　causes　of　processing　errors　after　wear　of　formed　milling　cutter,　a　complete　profile　equation　of　formed　milling　cutter　was　established　which　had　proper　rank　and　constant　clearance　angle.　Through　interference　checking　for　profile　equation　of　formed　milling　cutter,　the　correctness　of　profile　equation　was　ensured.　The　profile　equation　provides　a　theoretical　foundation　for　design　and　manufacture　of　the　formed　milling　cutter,　and　it　will　have　great　significance　to　actual　production.