An optical touch panel includes a substrate, a single planar light generator, at least a retro reflector device, and a single photo sensor array. The substrate has a surface. The single planar light generator is disposed outside the surface of the substrate for generating a planar light, where the illuminating range of the planar light covers the range of the surface of the substrate. The retro reflector device is disposed on a side of the substrate for reflecting the planar light. The single photo sensor array is disposed outside the surface of the substrate for sensing the reflected planar light and generating reflected light distribution information.