In the field of catalysis, the development of efficient and economical catalysts for the reduction of heavy metals such as Cr(VI) remains challenging. In this study, a series of CuCoOS nanomaterials were successfully prepared by a facile one-step method, and the morphological structures, elemental compositions, and optical properties of the catalysts were characterized in detail. The catalytic performance of each material was evaluated for reduction of a Cr(VI) solution in the dark without any other reagents. The CuCoOS catalyst exhibited excellent activity and completely reduced a 50 ppm Cr(VI) solution within 20 min. This activity could be mainly attributed to the large specific surface area of the prepared catalyst, which had many exposed active sites and defects. Synergy between the two metals (Cu and Co) also facilitated the catalytic reaction. The effects of the catalyst dose, concentration, and pH in the reduction system were studied systematically. Experiments performed by recycling the catalyst confirmed it had good stability and durability. Finally, a possible mechanism for Cr(VI) reduction is proposed.