To facilitate the analysis of the torque ripple form of BLDCM, the simplified model is used by most researchers, which will lead to the wrong conclusion that the torque could increase in some situations. This may cause the positive feedback in some systems and degenerate the control effect. Aimed at this problem, the mathematical formulas of the three-phase current in conducting and commutation period are derived in the case of 120 degree natural commutation mode. Then, the torque ripple formula is presented, and the fact that the commutation torque is bound to fall under the natural commutation is proved by the formula. To reduce torque ripple, the overlap commutation strategy is widely used. This paper analyzes and compares the advantages and disadvantages of all the overlap commutation strategies and selects the ON-PWM-PWM mode to reduce torque ripple. The accuracy of the torque ripple analysis and effectiveness of the torque ripple reduction of the proposed method are verified through the simulation and experimental results. This work is supported by National Natural Science Foundation of China (No. 51607083) and High-level Introduction of the Scientific Research Foundation Personnel of Nanjing Institute of Technology (No.YKJ201412).