A projection device, a projection system and a method for calibrating projected image are provided. The projection device and an external projection device the same image source and respectively project an image and another image corresponding to the image source. The same portion of the image source where the two images overlap each other forms an overlapping area. The projection device includes a lens, a light shielding member and a processor. The light shielding member is disposed on the lens. The processor controls the light shielding member to selectively shade a partial area of the lens according to the brightness of the image source, wherein the partial area corresponds to the overlapping area.