A touch detecting system for installation on a touch panel includes two point light sources arranged along one side of a touch panel, an optical sensor disposed at an opposite second side of the touch panel, at least one optical lens, and a processing unit. The at least on optical lens is disposed between the second side of the touch panel and the optical sensor. The at least one optical lens is spaced from the touch panel and the optical sensor, for directing the light from the point light sources to the optical sensor. The optical sensor captures an image which including two dark points of the light from the point light sources when a touch object is on the touch panel. The processing unit determines the position of the touch object on the touch panel based on positions of the dark points in the image.