Provided is a light source system, including: an excitation light source for emitting excitation light; a wavelength conversion device provided with a conversion layer which is used to perform wavelength conversion on at least a portion of the excitation light to obtain stimulated light, and to exit the stimulated light and the unconverted excitation light; and a dichroic assembly which is used to guide the stimulated light exited from the conversion layer to propagate along the second optical path, and finally to exit from the light source system along the exit optical path, and to guide at least a portion of the unconverted excitation light exited from the conversion layer to transmit on a path, which is not the exit optical path. Further provided is a projection device comprising the above light source system.