This paper describes torque ripple reduction in direct torque controlled Brushless DC Motor. The zero voltage vector in present most direct torque control technique is defined as the state when all switches are turn-off. However, in studying the circuit of the switch state in each sector, recognized the voltage of motor windings are not zero. Thus, six switch states corresponding to zero voltage vector as well as the rule to select zero voltage vector are proposed based on analyzing voltage vector one by one in each sector. Besides, the method of estimating electromagnetic torque according to stator current and back-EMF constant which is difficulty to off-line detect since, to most motors, neutral line of stator winding is not lead-out. So this paper adopts line back-EMF constant which is easy to detect off-line to estimate electromagnetic torque and give the formula. Finally, results of Matlab simulation and DSP experiment are given to verify the validity and feasibility.