In order to solve the problem of generalized design and batch processing of face gear, a method of tooth surface design and side milling of ruled-line face gears is proposed in this paper. First of all, the discrete points of the pitch cone surface of the face gear are calculated, and the straight-line cluster and section curve of the tooth surface are constructed to analyze the deviation of the ruled line face gear. Secondly, the tooth surface model of the ruled line face gear is constructed, and the curvature and contact trace are calculated. Thirdly, the curvature and tangent of the ruled line face gear tooth surface are analyzed, the feed plane of the equidistant surface and the guideline are obtained, the torsion angle of the tooth surface and the distribution of the tangent vector along the generatrix are calculated, and the tool axis position based on the two-point offset method is studied. Finally, the side milling processing test of the face gear is carried out, and the tooth surface of the face gear after side milling is measured. The measurement results verify the correctness of the tooth surface design and the side milling processing method of the ruled line face gear.