The invention provides a method for manufacturing a motor rotor and a self-aligning positioning mechanism used thereby. The method for manufacturing the motor rotor is characterized in that the motor rotor is formed by splicing a mandrel and magnetic steel by the self-aligning positioning mechanism through binding agent. The self-aligning positioning mechanism consists of a locating column, an aligning rod, an outer sleeve, a spring and a regulating rod, wherein the locating column contains a locating hole, communicating grooves are arranged around the upper part of the aligning rod, the sideof the aligning rod at the communicating grooves is a reversed-V-shaped conical surface which is matched with a corresponding reversed-V-shaped conical surface at the upper part of an inner cavity ofthe outer sleeve, and the lower part of the aligning rod is provided with a transverse through hole that is in clearance fit with a pressure bar; the outer sleeve is provided with an inner hole whichis in clearance fit with the aligning rod, the two sides of the outer sleeve are symmetrically provided with two long grooves, the pressure bar is inserted into the inner hole of the aligning rod andcan move up and down inside the two long grooves, the lower part of the outer sleeve is matched with the regulating rod by screw thread, and the spring is arranged between the aligning rod and the regulating rod. The invention has the advantages of greatly improving the accuracy of product and manufacturing efficiency as well as reducing the manufacturing cost of the product.