The disclosure relates to a projection device and a color gamut switching method thereof. The projection device includes a light source, a wavelength conversion element, an optical engine module, a projection lens module, and a filter element. The light source is configured to emit a first light beam. The wavelength conversion element is disposed on a transmission path of the first light beam, and the wavelength conversion element is configured to convert the first light beam into a second light beam. The optical engine module is disposed on a transmission path of the second light beam from the wavelength conversion element. The optical engine module is configured to convert the second light beam to form an image beam. The projection lens module is disposed on a transmission path of the image beam from the optical engine module. The filter element is removably disposed on the transmission path of the second light beam or the image beam.