The invention relates to a device and a method for torque ripple restraining of a permanent magnet brushless direct-current motor. The method includes: determining rotating speed operating modes of the motor; when the motor is in a low-speed operating mode during phase changing, reducing rise current in non-commutative windings under different states; when the motor is in a high-speed operating mode during phase changing, compensating drop current in the non-commutative windings under different states. The method has advantages that non-commutative torque ripple of the permanent magnet brushless direct-current motor in low-speed and high-speed operating modes can be restrained effectively to improve control precision and system stability of the permanent magnet brushless direct-current motor, operating efficiency of the motor is improved, and application range and application places of the permanent magnet brushless direct-current motor are expanded.