A projection system includes a light source, an image unit, a projection unit, a light-reflection unit and a screen. The light source emits a light beam. The image unit receives the light beam from the light source and forms an image light. The projection unit is disposed on the route of the image light. The projection unit receives the image light from the image unit and projects it out. The light-reflection unit disposed on the route of the image light has a reflecting layer and at least one light-pervious reflecting layer, and receives the image light from the projection unit. The light-pervious reflecting layer reflects the received image light to form a first image light. The reflecting layer reflects the received image light to form a second image light. The screen is disposed on the route of the first image light and the second image light. The first image light is projected on the screen to form a first image. The second image light is projected on the screen to form a second image. There is a displacement between the first and the second images.