Direct numerical simulation (DNS) of a turbulent channel flow is carried out to investigate the effect and mechanism of using spanwise oscillating Lorentz force to reduce boundary layer friction.We discussed the influence of Lorentz force intensity St and oscillating frequency T+ on the drag reduction effect and turbulent burst events. The results suggest the varying tendencies with St or T+ of the frequency of the turbulent bursts events are opposite to the intensity of the turbulent bursts events,and there exists an optimal parameter to achieve the largest amount of drag reduction.The composite effect of St and T+ can be well described by the equivalent spanwise wall velocity W+.