Turbulence control and drag reduction in a channel flow by using a steadily distributed spanwise Lorentz force are investigated numerically via a direct numerical simulation (DNS). The characteristics of controlled flow fields and vortex structures are described. Meanwhile, the mechanisms of turbulence suppression and drag reduction by the Lorentz force are also discussed. Calculated results indicate that: (1) The shear layers with a arge gradient of spanwise velocity are created in the laminar boundary layer induced by the spanwise Lorentz force, where the streamwise vortices are easily generated by perturbations. (2) Under the action of the distributed Lorentz force with proper control parameters, only periodically well-organized streamwise vortices are observed in the near-wall region of the turbulent channel flow. (3) After controlling, the averaged lift height of inclined streamwise vortices is reduced significantly as compared with the uncontrolled turbulence flow, resulting in the reduction of the burst strength and subsequent drag reduction on the wall.