A light source system comprises: a light-emitting device for emitting a first light and a second light in sequence; a beam splitting system with which the first light is divided into one beam in a first range of wavelength and the other beam in a second range of wavelength, respectively emitted along a first optical path and a second optical path, and also with which at least a part of the second light is emitted along the first optical path; a first spatial light modulator for modulating the beam emitted from the beam splitting system along the first optical path; a second spatial light modulator for modulating the beam emitted from the beam splitting system along the second optical path. The light source system has the advantages of high light-emitting efficiency and low cost. A projection system comprising the aforementioned light source system is also provided.