A circuit board includes an insulation layer, a signal layer disposed on one side of the insulation layer, and a ground plane and a power plane disposed on the insulation layer at a side opposite to the signal layer. The insulation layer forms a separating area arranged between the ground plane and the power plane. At least two signal traces parallel to each other are arranged on the signal layer at one side corresponding to one of the ground plane and the power plane. A width of the signal trace close to the separating area is wider than that of the signal trace away from the separating area.