A computer-based method and a computing device for checking signal transmission lines of a printed circuit board (PCB) layout are provided. The computing device identifies differential pairs in a currently run PCB layout according to an information file for the currently run PCB layout, checks whether any signal transmission line is routed between switching vias of each differential pair according to the information file for the currently run PCB layout, and displays a routing error window to display information of each misrouted signal transmission line.