A projection device, comprising: a light source system; a light valve, disposed on a transmission path of the illumination beam to convert the illumination beam into an image beam; and a projection lens, disposed on a transmission path of the image beam, converting the image beam into a projection beam; wherein the light source system of the projection device, comprising: a laser light source, providing a first light beam, and comprising a plurality of light-emitting units (LU1~LU8); a control circuit, coupled to the laser light source, configured to control a portion of the plurality of light-emitting units (LU1~LU8) to provide a light beam as the first light beam, and configured to detect electrical characteristics of the plurality of light-emitting units (LU1~LU8) providing the light beam, when characteristic parameters of the plurality of light-emitting units (LU1~LU8) providing the light beam as the first light beam do not reach the preset value, the control circuit is configured to control the projection device to project and display a light source selection interface that allows a user to select the light emitting units (LU1~LU8) that provide the light beam, the control circuit is configured to disable the plurality of light-emitting units (LU1~LU8) providing the light beam as the first light beam according to a light source selection command corresponding to the operation selected by the user, and is configured to control the remaining light-emitting units to provide the back-up light beam as the first light beam; a wavelength conversion device, disposed on a transmission path of the first light beam and converting a portion of the first light beam into a second light beam; and a light combining device, disposed on a transmission path of the first light beam (L1') and the second light beam, combining the first light beam (L1') the wavelength of which is not converted and the second light beam to generate an illumination beam. a light source system; a light valve, disposed on a transmission path of the illumination beam to convert the illumination beam into an image beam; and a projection lens, disposed on a transmission path of the image beam, converting the image beam into a projection beam; a laser light source, providing a first light beam, and comprising a plurality of light-emitting units (LU1~LU8); a control circuit, coupled to the laser light source, configured to control a portion of the plurality of light-emitting units (LU1~LU8) to provide a light beam as the first light beam, and configured to detect electrical characteristics of the plurality of light-emitting units (LU1~LU8) providing the light beam, when characteristic parameters of the plurality of light-emitting units (LU1~LU8) providing the light beam as the first light beam do not reach the preset value, the control circuit is configured to control the projection device to project and display a light source selection interface that allows a user to select the light emitting units (LU1~LU8) that provide the light beam, the control circuit is configured to disable the plurality of light-emitting units (LU1~LU8) providing the light beam as the first light beam according to a light source selection command corresponding to the operation selected by the user, and is configured to control the remaining light-emitting units to provide the back-up light beam as the first light beam; a wavelength conversion device, disposed on a transmission path of the first light beam and converting a portion of the first light beam into a second light beam; and