A projection touch system configured for detecting a position of a touch object and a projection touch method thereof are provided. The projection touch system includes an invisible light source, a projection panel and a light detector. The projection panel includes a transparent plate and a fluorescent film. An invisible light beam emitted by the invisible light source scans back and forth on the projection panel. A first fluorescent light beam and a second fluorescent light beam are emitted from the fluorescent film excited by the invisible light beam. When the touch object is touched to the projection panel, a portion of the invisible light beam is reflected to the fluorescent film, and the second fluorescent light beam is emitted. The light detector detects the second fluorescent light beam relative to the first fluorescent light beam by an intensity level to determine the position of touch object.