A light emitting device includes: an excitation light emitting source (71) for generating excitation light; a wavelength conversion device (72) comprising a wavelength conversion layer (722), the wavelength conversion layer (722) converting at least a part of the excitation light into converted light, and the converted light being light with a wide spectrum, or the converted light being mixed with excitation light not converted by the wavelength conversion layer (722) to form light with a wide spectrum; a driving device (73) for enabling the excitation light to move relative to the wavelength conversion layer; and a light splitting device (62) for splitting the light with the wide spectrum into at least two kinds of monochromatic light propagating along different paths. Further provided is a projection system comprising the light emitting device.