An illumination system is configured to provide an illumination beam. The illumination system includes at least one light source, a composite unit and an actuator. The at least one light source is configured to provide at least one light beam. The composite unit includes a diffusion surface and an optical surface opposite to each other, wherein the composite unit is disposed on a transmission path of the at least one light beam and configured to enable the at least one light beam to pass through. The actuator is connected to the composite unit for driving the composite unit to move along at least one direction, and the at least one direction is perpendicular to a normal direction of a plane on which the composite unit is located. A projection apparatus including the illumination system is also provided.