Abstract: The present invention concerns an optic projecting technique for a projecting system comprising a housing and a projector unit, the projecting system comprises a housing and a projector unit, wherein the housing is provided with a display screen and a plurality of optic elements in the housing; the system is characterized in that: the projector unit is placed on the back of the housing in favor of detachment and displacement; when the projector unit projects optic images into the housing, the images from the projector are reflected by the optic elements and projected to the rear side of the display screen; when the projector unit is placed outside of the housing, it directly projects the optic images to the display screen at a suitable distance away, thus a dual projecting system for rear projection and front projection can be is formed.