An optical touch system includes a touch panel and a reading circuit. The touch panel comprises a first touch area including a plurality of image sensing units, where the plurality of image sensing units is arranged to form an array of a plurality of columns and a plurality of rows. The reading circuit is coupled to the plurality of image sensing units, where the plurality of image sensing units includes a first selected image sensing unit and a second selected image sensing unit. The reading circuit reads the first selected image sensing unit in the first touch area in a first touch sensing frame, and the reading circuit reads the second selected image sensing unit in the first touch area in a second touch sensing frame.