After removing hob on CNC helical bevel gear milling machine with bevel gear with helical tooth, it machined not only the bevel gears or double curved surface gears, but also the cylindrical gears as well. While the cutter rotating and moving at one time, and forming the medium gear, gears machining was implemented with this method. Therefore, the coordination system that fixed on the medium gear and the cutter was introduced. When cutter rotates about x axis of the coordination system, the cone was formed, and the tooth of cylindrical gears was the envelope formed when the medium gear moving and the cylindrical gear rotating. The taper surface equations of the taper gears, tooth-coupling equations of bevel gears with helical tooth and the tooth surface equations were deduced at the same time.