An exemplary touch display system includes a flexible touch screen, a prism, an infrared light source, an infrared image sensor, and a processor. The prism is substantially isosceles right-angled triangular shaped, with a first side surface thereof being disposed adjacent to but spaced apart from back surface of the touch screen by air, wherein when a touch is applied to the touch display surface at a touch position, the touch screen is bent at the touch position and contact the prism at a contact position corresponding to the touch position. The infrared light source and the infrared image sensor are arranged adjacent to and facing to a hypotenuse surface of the prism. The processor is configured for processing image signals from the image sensor and obtaining the contact position based on light intensities of the image signals, thereby obtaining the touch position on the touch display surface.