1. A coordinate determining system for determining a screen coordinate of an indicating point shown on a screen, the coordinate determining system comprising: an image capturing module for capturing a plurality of images corresponding to the screen; a dividing module, coupled to the image capturing module, for dividing an overlapping image region of the images into a target image comprising a plurality of sub-regions; a determining module, coupled to the dividing module, for determining a position of the indicating point on the target image; and a converting module, coupled to the determining module, if the position of 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 converting the image coordinate into the screen coordinate according to a proportional parameter.