A motor assembling method is disclosed. The motor assembling method provides a base with a shaft tube, wherein the shaft tube has a thermoplastic positioning portion on an opening end thereof, and a shaft tube assembly is disposed into the shaft tube via the opening end. The motor assembling method further heats the thermoplastic positioning portion by a heating fixture to melt and deform the thermoplastic positioning portion until the opening end of the shaft tube has shrunk, wherein the shaft tube assembly is held in position in the shaft tube after the thermoplastic positioning portion has cooled down and solidified. The motor assembling method further couples a stator unit with an outer circumferential wall of the shaft tube, and couples a rotor with the shaft tube.