The present disclosure provides a light source system and a projection device. The light source system includes: a laser light source, a supplementary light source, a wavelength conversion device and an imaging subsystem. The laser light source is configured to emit laser light. The supplementary light source is configured to emit supplementary light. The wavelength conversion device is configured to convert the laser light into excited light and output first light including the excited light and the laser light. The imaging subsystem is configured to form a first light imaging beam, a supplementary light imaging beam, and a mixed light imaging beam; the imaging subsystem includes a light combining device and a reflective assembly, the light combining device is placed at an intersection of the first light imaging beam and the supplementary light imaging beam, and the reflective assembly is placed between the wavelength conversion device and the light combining device.