A circuit board for transmitting a high speed signal and for the high speed signal to be detected comprises a substrate, an insulating layer and two metal printed wires. The insulating layer is disposed on the substrate, and comprises a first surface, a second surface and a test opening, with the first surface facing away from the substrate, the second surface facing the substrate, and the test opening passing through the first surface and formed above the second surface. Said two metal printed wires are configured to transmit the high speed signal and embedded in the insulating layer between the first surface and the second surface. At least one of the metal printed wires comprises a test section which is aligned to the test opening of the insulating layer and exposed by the test opening.