An optical rotating device includes a substrate having a first surface and a second surface opposite to each other, a rotating shaft connected to the substrate, a driving element connected to the rotating shaft and driving it to rotate, a wavelength conversion layer disposed on the first surface to convert a first laser beam into a converted beam, and a polarizing element disposed on the second surface. The first laser beam and at least one second laser beam are respectively transmitted to the wavelength conversion layer and the polarizing element from opposite directions. The driving element drives the substrate, the wavelength conversion layer and the polarizing element to rotate along the rotating shaft as a rotation central axis. When the polarizing element is rotated, the polarizing element makes the second laser beam have different polarization states at different times. An illumination system and a projection device are also provided.