A projection system may include a lamp irradiating a light, an illumination unit providing a plurality of lenses on light paths, a composition unit providing an image by separating/composing the light, a projecting lens projecting the light composed in the composition unit to a screen, a cool air injection guide provided to one side of the composition unit for guiding an air injection port to be injected into the composition unit, and an injection port guide interposed on a contact portion of the cool air injection guide and the composition unit. The injection port guide may be formed in plate-shape. An injection port may be formed on the injection port guide to eject the air to the composition unit. A fan may be formed on other side of the composition unit for transmitting a negative pressure to the side of the composition unit.