Conical twin-screw is the key part of conical twin-screw extruder,and the machining precision of that directly affects the meshing of conical twin-screw and extruder's performance.This paper researches the state of the art of machining conical twin-screw and proposes a new method to machine conical twin-screw on NC milling machine,which machines conical twin-screw with vertical tooth form based on the analysis of conical twin-screw geometric contour and meshing characters and through NC program generated by an automatic programming system.The research result advances the production efficiency of conical twin-screw and has a broad engineering significance.