Aiming at the problem of non-commutation torque ripple of brushless DC motor，this paper analyzesthe cause of the non-commutation torque ripple in detail，and points out that the diode freewheeling of the inactivephase is an important factor which leads to the non-commutation torque ripple. This paper analyzes the non-commu-tation torque ripple which is caused by the diode freewheeling of the inactive phase in four modulation modes. Itpoints out that the time of the torque ripple is different in different modes of modulation. It deduces and validatesthat the non-commutation torque ripple of brushless DC motor is decreased by using PWM_ON_PWM. UsingTMS320F2812 DSP as the core of control and using rated 180W brushless DC motors as the object of control，andcontrolling the speed and current dual-closed-loop. It measures the waveforms of phase current were measured indifferent PWM modulation modes. The experimental results prove that PWM_ON_PWM can absolutely inhibit thenon-commutation torque ripple which is caused by the diode freewheeling of the inactive phase.