An optical projection device includes a laser engine, a first wave plate and a lens. The laser engine provides light. The first wave plate changes a light phase. The lens focuses light. A projecting method of an optical projection device includes providing a light including a first P polarized light, a first S polarized light, and a second S polarized light, and projecting light through a wave plate on a screen, wherein the wave plate moves in a direction perpendicular to light. A projecting method of an optical projection device includes providing light including a first P polarized light, a first S polarized light, and a second S polarized light, and projecting light through a wave plate on a screen, wherein the wave plate rotates around an axis parallel to a projecting direction of light.