The inventiondiscloses a light emitting device and a related projection system. The light emitting device comprises an excitation light source used for generating excitation light, a wavelength conversion device comprising a wavelength conversion layer, a driving device and a sealing device, wherein the wavelength conversion layer absorbs the excitation light and emits excited light, the driving device drives the wavelength conversion layer to realize periodic rotation to enable an incident light spot in the wavelength conversion layer to do motion in the predetermined circle locus, a line speed of at least a partial region of the wavelength conversion device is greater than or equal to 75m/s, the sealing device comprises a light penetration region and a heat conduction region, the wavelength conversion device is arranged in the sealing device, the emitting light of the wavelength conversion device penetrates through the light penetration region, a distance between the heat conduction region and a light emitting face of the wavelength conversion device or an opposite surface is smaller than or equal to 1mm, heat is conducted outside the sealing device, and the area of the heat conduction region is greater than or equal to the area of the incident light spot of the excitation light. The light emitting device having a dust-proof function and a function of effective work temperature reduction of the wavelength conversion device, and the related projection system are provided.