A printed circuit board layout method includes the following steps. A printed circuit board with a signal layer, and a pair of differential transmission lines positioned on the signal layer is provided. A first distance is determined, when the distance between the pair of differential transmission lines is greater or less than the first distance, an eye width and an eye height of an eye diagram obtained at output terminals of the pair of differential transmission lines increases. A second distance less than the first distance is set between the pair of differential transmission lines which makes the eye width and the eye height meet requirement of the differential transmission lines for the eye diagram.