Ce/SiO2 composited cross‐linked chitosan (C‐CTS‐S), SiO2 composited cross‐linked chitosan (CTS‐S) and Ce composited cross‐linked chitosan (C‐CTS) flocculation materials are successfully synthesized. The structure along with the decolorization performance and mechanism of treating tartrazine dye wastewater are studied. The results show that the prepared materials are new composites rather than the mixture of the raw agents. Some silica species embed in the matrix or stay on the surface of chitosan (CTS) during the compositing process, and form hydrogen bonds with –NH2 or –OH of CTS. Besides, Ce participate coordination with –NH2 and –OH of CTS. C‐CTS‐S has disorder, unobvious porous and loose sheet‐like structure with smaller particles and positive charge. It shows high performance of tartrazine dye decolorization over a wide range of pH, and produces little sewage sludge after flocculation, providing a favorable condition for later processing. In addition, the possible decolorization mechanism is mainly electroneutralization adsorption and the synergistic effect of deposition netting and bridge aggregation. [ABSTRACT FROM AUTHOR]