Manufacturing method of screw rotor and double screw rotor

The invention provides a manufacturing method of a screw rotor. The screw rotor manufactured by the method comprises a main rotor body and multiple rotor sub-bodies, a transmission shaft is arranged on the main rotor body, all the rotor sub-bodies are provided with mounting holes, the transmission shaft is connected in the mounting holes of all the rotor sub-bodies in an inserted manner, expansion sleeves are arranged between the mounting holes of all the rotor sub-bodies and the transmission shaft, the main rotor body and the rotor sub-body adjacent to the main rotor body are tightly spliced, any two adjacent rotor sub-bodies are tightly spliced, and tooth-shaped molded lines at the splicing positions are kept coherent. The screw rotor is decomposed and manufactured separately, the technical requirements for a screw rotor machine tool are reduced, and the machining and manufacturing time of the screw rotor is also shortened; and the requirements of the expansion sleeves for the machining and cooperation prec