A novel Fenton reagent, chalcopyrite CuFeS2 nanocrystals (NCs) with an average diameter of 10.6 +/- A 1 nm are synthesized by a facile solution phase method in a standard Schlenk Line, and they can efficiently degrade organic dyes (methylene blue, rhodamine B and rhodamine 6G) aqueous solution (100 mg L-1) within 1 min. XRD and TEM have been carried out to determine the crystal information, size, and shape of CuFeS2 NCs. The degradation process is investigated by UV-Vis spectroscopy, and its advantage is illustrated by comparing with bulk chalcopyrite. X-ray photoelectron spectroscopy is used to discuss its degradation mechanism. Based on this Fenton reagent, CuFeS2 NCs/biomass composite degradation column is made using sawdust as substrate, and it can efficiently degrade organic dyes continually (the total amount of organic dyes degraded by the column are 8.67, 8.44, and 8.64 times the amount degraded by pure CuFeS2 NCs, respectively).