An illumination system for providing an illumination beam to a light valve is provided. The illumination system includes a light source, a light integration rod, a color wheel, a first focusing unit and a second focusing unit. The light source is capable of generating the illumination beam, and the light integration rod is disposed on the transmission path of the illumination beam. The first focusing unit is disposed between the integration rod and the color wheel and is capable of focusing the illumination beam onto the color wheel. The second focusing unit is disposed between the color wheel and the light valve and is capable of focusing the illumination beam onto the light valve.