There is provided an optical engine of a projection system comprising: a lamp irradiating light; an illumination unit provided with a plurality of lens through which the light is passed; a composition unit separating and composing the light to form an image signal; an engine base provided with the illumination unit and the composition unit on a top portion thereof; a reinforcing part which is made of a high intensity material and which is provided between the composition unit and the engine base to prevent a deformation of the composition unit; and a projection lens projecting light composed in the composition unit to the screen. Therefore, it is possible to stably embody a high definition image in the optical engine of the projection system.