A method for automatically detecting and switching video signals on a monitor has steps of storing multiple menu groups in the monitor and executing a resolution identifying mode. Each menu group has multiple similarly public resolutions. The resolution identifying mode has acts of determining whether the video resolution of the video signal matches one of the resolutions in one of the menu groups and creating a launch menu to show all the resolutions in the menu group having the resolution matched to the video resolution of the video signal when the video resolution of the video signal matches one of the resolutions in one of the menu groups. Therefore, the method solves the problem of misapplying resolutions on the conventional monitor.