An illumination system having improved efficiency and uniformity for an image projection apparatus. The illumination system is employed for supplying an optical radiation beam along a principal axis to illuminate an object which, in a plane perpendicular to the principal axis, has a non-round cross-section. The illumination system includes: a light source for emitting light beams; a reflective mirror, having a plurality of reflective curved surfaces for reflecting the light beams emitted from the light source to form a plurality of reflective beams; and a lens plate, having a plurality of lenses, each of the plurality of lenses corresponding to a reflective curved surface of the reflective mirror to project the plurality of reflective beams onto the object, so that the plurality of reflective beams are superimposed on the object and produce a uniform illumination.