The present invention suggests a simplified and robust scanning method as a scenario for scanning video sources of a display device such as a TV or projector. The inventive method is attained by way of grouping the video sources and prioritizing the scanning priority for each video source group in terms of the viewing time statistic or the frame number statistic of each video source group. Therefore, the display device is capable of scanning each video source group based on the scanning priority to discover if there is a video signal inputted into the video source.