A system for physical-distancing detection in a specified area includes a locator locating a positioning quadrangle plane in a specified area; an image-capturing device obliquely capturing an image of the specified area to generate a captured image of the specified area; and a coordinate converter defining a coordinate conversion function according to raw coordinates of selected points of the positioning quadrangle plane in the captured image of the specified area and reference coordinates of the selected points of the positioning quadrangle plane in an overlooked image of the specified area. The image-capturing device converts raw coordinates of the captured image of the specified area into converted coordinates of the overlooked image of the specified area by way of the coordinate conversion function, determines a physical-distancing condition between two persons according to the converted coordinates, and automatically takes an action corresponding to the physical-distancing condition.