A projection device includes a laser source and a birefringent depolarizer. The birefringent depolarizer is a single wedge shape and is arranged in front of a projection lens. The laser source is configured to emit a laser beam to penetrate the birefringent depolarizer to be a projection beam having multiple polarization patterns different from polarization patterns of the laser beam. The projection beam is projected onto a projection screen through the projection lens. The polarization patterns are multiple different polarization directions.