Spindle motor capable of automatically locking grinding wheel

The invention discloses a spindle motor capable of automatically locking a grinding wheel. The spindle motor comprises a motor, a motor rotating shaft is installed in the motor, a rotating shaft through hole penetrating in the axial direction is formed in the motor rotating shaft, a flange is coaxially connected to the motor rotating shaft at the front end of a motor front cover in a sleeving mode and fixed to the motor rotating shaft, and a rotating shaft conical part is coaxially formed at the front end of the motor rotating shaft; an expansion sleeve is further included, an expansion sleeve conical hole matched with the rotating shaft conical part is coaxially formed in the expansion sleeve in the axial direction, the rotating shaft conical part is inserted into the expansion sleeve conical hole, and the outer wall of the expansion sleeve is coaxially connected with a detachable grinding wheel in a sleeved mode. A pull rod capable of linearly reciprocating is axially arranged in the rotating shaft through