The invention discloses a motor assembly for an air compressor and a motor machining process for a motor assembly. The motor assembly is technologically characterized in that the motor assembly comprises a rotating shaft and a rotor which is mounted on the rotating shaft; the rotating shaft is a cylindrical polished rod; the middle part of the rotating shaft is provided with a hobbing area which is used for snapping with the rotor in an embedded manner. Two sides of the hobbing area are provided with positioning holes for positioning a bearing. One end of the rotating shaft is provided with a recessed trough for connecting with a fan, and the other end is provided with connecting holes which are used for connecting with a crankshaft. Through changing the structure design of the rotating shaft, the rotating shaft satisfies an original structure requirement, and higher convenience and higher speed are obtained in machining. Furthermore the raw material cost and the machining cost of the whole motor assembly can be greatly reduced.