Torque ripple reduction of the brushless DC motor has been the main issue of the servo drives in which the speed fluctuation and the vibration should be minimized. Un-ideal back EMF (electromagnetic force) usually induces distinct torque ripple. A full EMF feedback strategy is presented in order to effectively reduce torque ripple. The relationship between the terminal voltage of auxiliary winding and the back EMF of brushless DC motor are investigated, and the back EMF can be measured on-line by using the auxiliary winding, the q-axis current for a constant torque to produce is calculated through coordinate transformation when d-axis current is zero, and the reference q-axis current is adjusted in real time by vector control in dq0 coordinate. The simulation results show that the proposed strategy can effectively minimize the torque ripple.