The invention relates to a manufacturing method for a ternary impeller of a compressor, in particular to a milling method for a ternary impeller with large diameter. The method comprises the following steps: generating a data file from the blade type and hub data of the calculated ternary impeller with large diameter, and inputting the data file into an operation platform; defining the rotating direction of blades, the quantity of the blades, a blade fillet and a blade round head manner; carrying out three-dimensional entity modeling by using the existing operation platform to generate an impeller ternary model file; clamping an impeller blank on a work table of a five-axle numerical control manufacturing center; linking three linear axles and fixing two rotating axles; firstly milling the welding line of the slot body of the short blade, and welding the short blade; after vacuum stress relieving, milling the welding line of the slot body of the long blade; and welding the welding line of the slot body of the long blade and milling the welding line. In the invention, the process time of the impeller is shortened; and compared with the traditional processing method, the process time can be shortened by more than twice, the cost of the cutter is reduced by eight folds, and the service life of machine tool is greatly prolonged.