A signal transmission line check method to be executed by a computing device is described. A to-be-checked signal transmission line group in a displayed printed circuit board (PCB) layout is determined. Whether all signal transmission lines of the to-be-checked signal transmission line group are laid out in a same layer of the displayed PCB layout is checked according to an input serial number of a chipset and layer properties of the to-be-checked signal transmission lines. The signal transmission lines that do not satisfy design standards are determined when not all of the to-be-checked signal transmission lines are laid out in a same layer. A related computing device is also disclosed.