An illumination system, comprising: a blue light source, adapted to provide a blue light beam; an excitation light source, adapted to provide an excitation beam; a first dichroic element, disposed on transmitting paths of the blue light beam and the excitation beam; a wavelength converting element, disposed on the transmitting path of the excitation beam, and adapted to convert the excitation beam into an excited beam, wherein the excitation beam passes through the first dichroic element to the wavelength converting element and is converted into the excited beam, the excited beam is transmitted to the first dichroic element and reflected, a wavelength of the blue light beam is greater than a wavelength of the excitation beam, and the blue light source and the excitation light source are disposed on the same side of the first dichroic element; and a filter element, disposed on the transmitting paths of the blue light beam and the excited beam, the filter element comprising a first filter section, a second filter section and a diffusion section, wherein at a first timing period, the blue light source is in an off state or a power-saving state, the excitation beam is transmitted to a first converting section of the wavelength converting element to be converted into a first exited beam, and the first excited beam passes through the first filter section to generate a first red light beam, at a second timing period, the blue light source is in the off state or the power-saving state, the excitation beam is transmitted to a second converting section of the wavelength converting element to be converted into a second excited beam, and the second excited beam passes through the second filter section to generate a green light beam, at a third timing period, the excitation light source is in the off state or the power-saving state, and the blue light beam passes through the diffusion section, wherein the excited beam comprises the first excited beam and the second excited beam. a blue light source, adapted to provide a blue light beam; an excitation light source, adapted to provide an excitation beam; a first dichroic element, disposed on transmitting paths of the blue light beam and the excitation beam; a wavelength converting element, disposed on the transmitting path of the excitation beam, and adapted to convert the excitation beam into an excited beam, wherein the excitation beam passes through the first dichroic element to the wavelength converting element and is converted into the excited beam, the excited beam is transmitted to the first dichroic element and reflected, a wavelength of the blue light beam is greater than a wavelength of the excitation beam, and the blue light source and the excitation light source are disposed on the same side of the first dichroic element; and a filter element, disposed on the transmitting paths of the blue light beam and the excited beam, the filter element comprising a first filter section, a second filter section and a diffusion section, wherein at a first timing period, the blue light source is in an off state or a power-saving state, the excitation beam is transmitted to a first converting section of the wavelength converting element to be converted into a first exited beam, and the first excited beam passes through the first filter section to generate a first red light beam, at a second timing period, the blue light source is in the off state or the power-saving state, the excitation beam is transmitted to a second converting section of the wavelength converting element to be converted into a second excited beam, and the second excited beam passes through the second filter section to generate a green light beam, at a third timing period, the excitation light source is in the off state or the power-saving state, and the blue light beam passes through the diffusion section, wherein the excited beam comprises the first excited beam and the second excited beam.