A flat heat pipe includes a flat hollow pipe and a capillary structure. The flat hollow pipe has a first flat portion, a second flat portion and two arc portions, wherein the two arc portions are connected to both sides of the first and second flat portions. The capillary structure is formed in the flat hollow pipe. The capillary structure has a central portion and two edge portions, wherein the central portion is located on an inner wall of the first flat portion, the two edge portions are located on inner walls of the two arc portions respectively, and a thickness of the central portion is smaller than a thickness of each of the two edge portions.