The invention relates to a double-layer capacitor comprising a positive current collector, a positive active material, a porous insulator layer, a negative current collector, and a negative active material, wherein the porous insulator layer has a porous three-dimensional grid structure and is immersed into an electrolyte; one side of the porous insulator layer is filled with an active material while the other side of the porous insulator layer is not filled with the active material, or both sides of the porous insulator layer are filled with the active material while the middle of the porous insulator layer remains a state without the active material so as to enlarge the contact area between the active material and the electrolyte and shorten the distance between the positive and negative active materials, thereby increasing the specific capacitance of the double-layer capacitor and reducing equivalent series resistance.