An optical system (200, 200d, 200e, 200f), comprising: a light source configured to emit an illumination beam; a filtering module disposed on a transmission path of the illumination beam and comprising a plurality of filtering units (222, 224, 226) of different colors, the filtering units (222, 224, 226) moving into the transmission path of the illumination path in turn, wherein each of the filtering units (222, 224, 226) are adapted to reflect a part of the illumination beam and to allow another part of the illumination beam to pass through; a wavelength conversion unit (260a, 260b, 260c, 260d) disposed on a transmission path of the part of the illumination beam reflected by at least one of the filtering units (222, 224, 226) and configured to convert the part of the illumination beam reflected by the at least one of the filtering units (222, 224, 226) into a converted beam (216a, 216b, 216c); and a reflection unit (250, 250f), wherein the wavelength conversion unit (260a, 260b, 260c, 260d) is disposed on the reflection unit (250, 250f), the reflection unit (250, 250f) being adapted to reflect the converted beam (216a, 216b, 216c) to the at least one of the filtering units (222, 224, 226), such that at least a part of the converted beam (216a, 216b, 216c) passes through the at least one of the filtering units (222, 224, 226), wherein the reflection unit is a concave mirror configured to converge the converted beam (216a, 216b, 216c) on the at least one of the filtering units (222, 224, 226), and the optical axis of the light source is tilted relative to the filtering units (222, 224, 226) and the optical axis of the reflection unit (250, 250f) is tilted relative to the filtering units (222, 224, 226). a light source configured to emit an illumination beam; a filtering module disposed on a transmission path of the illumination beam and comprising a plurality of filtering units (222, 224, 226) of different colors, the filtering units (222, 224, 226) moving into the transmission path of the illumination path in turn, wherein each of the filtering units (222, 224, 226) are adapted to reflect a part of the illumination beam and to allow another part of the illumination beam to pass through; a wavelength conversion unit (260a, 260b, 260c, 260d) disposed on a transmission path of the part of the illumination beam reflected by at least one of the filtering units (222, 224, 226) and configured to convert the part of the illumination beam reflected by the at least one of the filtering units (222, 224, 226) into a converted beam (216a, 216b, 216c); and a reflection unit (250, 250f), wherein the wavelength conversion unit (260a, 260b, 260c, 260d) is disposed on the reflection unit (250, 250f), the reflection unit (250, 250f) being adapted to reflect the converted beam (216a, 216b, 216c) to the at least one of the filtering units (222, 224, 226), such that at least a part of the converted beam (216a, 216b, 216c) passes through the at least one of the filtering units (222, 224, 226), wherein the reflection unit is a concave mirror configured to converge the converted beam (216a, 216b, 216c) on the at least one of the filtering units (222, 224, 226), and the optical axis of the light source is tilted relative to the filtering units (222, 224, 226) and the optical axis of the reflection unit (250, 250f) is tilted relative to the filtering units (222, 224, 226).