Abstract: An optical projection system includes a bottom cover, a foundation flat plate, at least one supporting element, a light source module, and an optical engine module. The bottom cover includes a bottom plate and two opposite side plates. The side plates are respectively connected with two ends of the bottom plate. The side plates and the bottom plate form an accommodating space. The foundation flat plate located between the side plates is disposed on the bottom plate. The foundation flat plate is apart from the side plates. The supporting element is disposed on the foundation flat plate. The light source module is disposed on the foundation flat plate. The optical engine module is disposed on the supporting element. The foundation flat plate, the supporting element, at least part of optical engine module, and at least part of the light source module are disposed in the accommodating space.