A novel synthesis of CdS 1− x Se x solid solution is presented, which is based on the room temperature reaction among CdO(CdCO 3, CdCl 2), Na 2S·9H 2O and Se powders. XRD and composition analysis results show that the composition of CdS 1− x Se x is related to the Cd sources. Namely, CdS 0.54Se 0.46 has been obtained from CdO precursor, and CdS 0.75Se 0.25 has been obtained from CdCO 3 or CdCl 2 precursors. The excess Na 2S·9H 2O plays crucial role for the formation of CdS 1− x Se x , by which the solid phase reaction mechanism has been discussed. The optical properties of CdS 0.54Se 0.46 and CdS 0.75Se 0.25 were characterized by absorption spectrum and fluorescent spectrum, respectively. The average sizes of particles are about 1.67–2.49 μm by the Ls601-Laser particle analysis instrument measurement.