Red non-toxic and environmentally friendly γ-phase cerium sulfide powders have promising applications in the fields of coatings, outdoor displays and smart buildings. However, the development of an environmentally friendly preparation process and the improvement of production efficiency of cerium sulfide powders remain major challenges. In this study, eco-friendly γ-Ce2S3 powders with excellent color properties have been produced by adding ammonium thiocyanate to the precursor of cerium without H2S or CS2. The effect of impurities (mainly Ce2O2S) with different amounts on spectral properties of cerium sulfide powders has been studied through chemical and physical methods. In addition, the significance of impurity doping on the reaction synthesis was studied by combining detailed experimental characteristics with density functional theory calculations. The results show that the reduction of impurity content can greatly improve the chromaticity value of γ-Ce2S3 and change color from dark red to bright red.