The invention relates to a rotor of a single-shaft centrifugal compressor. The rotor comprises a spindle with a conical shaft head, and an impeller matched with the shaft head. The invention further discloses an assembly method of the rotor of the single-shaft centrifugal compressor. The rotor structure assembled through the assembly method, of the single-shaft centrifugal compressor, is simple in assembly technology and high in assembly precision, and has the characteristics of being high in transmission torque and free of relative displacement, operation stability of the rotor is greatly improved, vibration amplitude of the rotor during the operation process is decreased, and a user maintains the compressor in the later period quite easily and conveniently.