In this paper, the effect of Halo concentration on performance of 30 nm gate length Double-Gate MOSFET with 30 nm thin body-Si is investigated by using two dimensional device simulator. We quantitatively show the dependency of electrical characteristic (subthreshold-slope, threshold voltage: Vth, drivability and leak current: Ion and Ioff) on the Halo concentration. This dependency can be explained by the reasons why the Halo concentration has directly effect on the potential distribution of the body. It is made clear that from viewpoint of body potential control, the design of Halo concentration is key technology for suppressing short-channel effect and improving subthreshold-slope, Ion and Ioff adjusting the Vth.