Abstract: Tiled displays systems built by combining the images from arrays of rear projection cubes can provide huge numbers of pixel elements to applications needing to visually represent lots of information. It is, however, puzzled by the gaps between adjacent cubes, the gaps is viewed as black lines in the displaying picture. The reason of the black lines is analyzed and the solution of eliminating the black lines is proposed. By zooming in the projection image, the edging projection rays are led into the gaps using optical wedge at screen border. The rays strike out lateral surface of screen with approaching total inner reflection angle and refractive then incident normally to the screen. The experiment indicates the picture can be displayed through the gaps without any black or gray lines.