Abstract: A single-projection widescreen projecting device includes an image processing system and in turns in the direction of light path an optical non-imaging system providing a light source; an optical imaging system; a light path switching system; and a projecting lens which projects a magnified image onto a screen. The image processing system connects the optical imaging system to the light path switching system and is used to divide the image into N frames of small images and then transmit the small images to the optical imaging system. N is natural numeral greater than 1. At the moment of transmitting the small images to the optical imaging system, a corner signal corresponding to each frame of the small images is transmitted the light path switching system. The optical imaging system is used to receive N frames of the small images and light rays from the optical non-imaging system and then display the N frames of the small images after the light rays of the optical non-imaging system are adjusted.