This paper made an experimental study of Cr(Ⅵ)-bearing wastewater treated by natural pyrite. XPS peaks of Cr2p apparently appeared on the pyrite surface and colloidal precipitates during and after the reaction, which can be fitted into three peaks at different binding energies of 574.7～575.1 eV, 576.6～576.9 eV and 578.2～578.7 eV. The relative peaks represent the phases of Cr2S3, Cr2O3 and CrO3, respectively. The precipitate phase of Cr2S3 was found for the first time in this experiment. The results show that the phase of chromium-bearing sulfides can be produced in aqueous media under the conditions of room temperature and normal ambient pressure. Taking full advantage of this chromium-bearing sulfide phase, we can utilize natural pyrite including pyrrhotite to transfer Cr (Ⅲ) precipitates directly into colloidal precipitates without adding base in the process of reducing Cr(Ⅵ). The content of totalchromium in the upper treated supernatant is lower than that of the National Standards of Sewage Treatment. The heavy metals dissolved by natural pyrite itselfare very low in content so that they don't affect the effluent quality. In order to apply and extend the new technology for one-step treatment of Cr(Ⅵ)-bearing wastewater in which Cr(Ⅵ) was reduced and Cr (Ⅲ) was precipitated simultaneously by natural pyrite and pyrrhotite, we should exploit and apply chromium-bearing precipitate phase.