The invention provides a one-time clamping four-shaft linkage rotary milling molding method for numerical control blade roots. The method can effectively reduce the field debugging workload of workers and improve the processing efficiency; and a blade root molding cutter is not needed, so that the cutter loss is reduced and the processing cost is reduced. A four-shaft horizontal processing centeris adopted, and the blade root profile processing cutter is a big spiral angle dense teeth milling cutter. The method comprises the following processing steps of: (1) setting a processing programmingorigin in a blade root UG model of a gas compressor; (2) calculating cutter loci of each plane and each curved surface of blade roots according to the processing programming origin, and generating a cutter location file; (3) measuring the position of the processing programming origin relative to the rotary center of a horizontal lathe on site, and obtaining values of X axis and Z axis between thetwo points; and (4) inputting the X-axis and Z-axis values of the on-site measured processing programming center origin relative to the rotary center of the horizontal lathe to the software of a horizontal rotary milling program conversion system, calculating an NC code file of the rotating cutter locus relative to the lathe, and performing profile processing of the blade roots of the gas compressor.