1. An interactive display system, comprising: an image provider, providing a display image; and a ranging apparatus, comprising: an image sensor; an imaging lens, configured to image an object on the image sensor to produce an image of the object having a plurality of image parameters onto the image sensor, wherein the image parameters change differently with change of an object distance of the object, and the image sensor converts the image of the object into an signal; and a processor, configured to determine whether the object is within a predetermined object distance range according to the signal and different changes of the image parameters with the change of the object distance, and when the processor determines that the object is within the predetermined object distance range, the processor determines that the object touches the display image.