Provided is a projection system, a light source system, and a light source assembly. The light source system (100) comprises an excitation light source (101), a wavelength conversion device (106), a color filtering device (107), a drive device (108), and a first optical assembly. The wavelength conversion device (106) comprises at least one wavelength conversion region. The optical filtering device (107) is fixed face-to-face with the wavelength conversion device (106), and comprises at least a first optical filtering region. The drive device (108) drives the wavelength conversion device (106) and the optical filtering device (107), 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.