The invention belongs to the technical field of motor cooling systems, and provides a semi-closed permanent magnet motor cooling system in order to solve the problems that the cooling effect cannot beguaranteed, and no scrap iron or dust enters a strong magnetic rotor of a motor under the condition that the operation environment of the motor is severe. The system comprises a rotor, a rotating shaft, a casing, a stator core, a stator winding, an air inlet hole, an air outlet hole and a rotor sleeve structure, and the rotor sleeve structure sleeves the rotor to isolate the rotor from a stator;and the air inlet hole and the air outlet hole separately penetrate through an end cover arranged on the casing. In the working process, the external cooling air is guided in through the air inlet hole, flows through the stator winding at the end part of one side of the motor, the cooling channel on the stator iron core and the stator winding at the end part of the other side of the motor and thenflows out through the air outlet hole so as to cool the semi-closed permanent magnet motor. According to the present invention, foreign matters can be prevented from entering the rotor, and the cooling effect of the motor is not affected.