provided is a projection system , a light source system , and a light source assembly . the light source system comprises an excitation light source , a wavelength conversion device , a color filtering device , a drive device , and a first optical assembly . the wavelength conversion device comprises at least one wavelength conversion region . the optical filtering device is fixed face - to - face with the wavelength conversion device , and comprises at least a first optical filtering region . the drive device drives the wavelength conversion device and the optical filtering device , allowing the wavelength conversion region and the first optical filtering region to act synchronously , and the wavelength conversion region is periodically set on the propagation path of the excitation light , thereby converting the excitation light wavelength into converted light . the first optical assembly allows the converted light to be incident on the first optical filtering region . the first optical filtering region filters the converted light , so as to enhance the color purity of the converted light . the light source system is simple in structure , easy to implement , and highly synchronous .