The invention belongs to the field of manufacturing of a gear or a rack, particularly the field of tooth manufacturing on a gear with varying working radius, and relates to a constant rotation speed non-circular gear hobbing method with an automatic setting angle adjustment function for a gear billet. The method comprises a five-axis four-linkage scheme and a six-axis five-linkage scheme, wherein the setting angle of a hob can be automatically adjusted by an independent numerical control axis, and the automation degree and the adjustment accuracy are higher. Four-linkage in the five-axis four-linkage scheme is that with constant gear billet rotation speed, Y-axis speed and rotation speed of a hob are in linkage according to generating movement relative to the rotation speed of the gear billet, and the Z-axis speed is linked linearly relative to the rotation speed of the gear billet; and five-linkage in the six-axis five-linkage scheme is that with constant gear billet rotation speed, the Y-axis speed, X-axis speed and the rotation speed of the hob are in linkage according to the generating movement relative to the rotation speed of the gear billet, and the Z-axis speed is linked linearly relative to the rotation speed of the gear billet. According to the method, the constant rotation speed of the gear billet, which is used as a reference frequency, is lower, the requirement on a detection element is lower, and the detection accuracy is higher. The method can be used for numerical control gear hobbing of non-circular straight/bevel gears and elliptical type straight/bevel gears.