A coordinate determining system is disclosed. The coordinate determining system comprises an image capturing module, a dividing module, a determining module, and a converting module. The image capturing module is used for capturing a plurality of images corresponding to the screen. The dividing module is used for dividing an overlapping image region of the images into a target image comprising a plurality of sub-regions. The determining module is used for determining a position of the indicating point on the target image. If the indicating point is in a target sub-region among the sub-regions and has an image coordinate relative to an original of the target sub-region, the converting module will convert the image coordinate into the screen coordinate according to a proportional parameter.