In this work, an environmentally friendly polydopamine-modified dialdehyde chitosan (PDA/DCS) was synthesized by the polydopamine (PDA) grafted with dialdehyde chitosan (DCS). The DCS was prepared via sodium periodate selective oxidation of the chitosan (CS). In order to characterize the micro morphology and chemical structure of the modified chitosan, SEM, FTIR, and other tests were performed. The adsorption abilities were studied using the carmine as a model pollutants. As the results revealed, the CS molecular was produce the covalent binding with PDA due to the formation of the aldehyde group by sodium periodate oxidation reaction. A key factor in the improved adsorption abilities of DCS and PDA/DCS was the selective oxidation treatment. Compared with the pristine CS, the crystallinity of DCS dropped sharply, while the porosity and specific surface area were increased. In addition, the microstructure of PDA/DCS presents a dense porous structure. The adsorption processes of DCS and PDA/DCS both followed the quasi-second-order kinetic equation and Langmuir isothermal model. Moreover, the adsorption rate and capacity of PDA/DCS were significantly enhanced in comparison to the DCS. When the initial mass concentration of dye is 700 mg/L, the maximum monolayer adsorption capacity of PDA/DCS was 1194.4 mg/g. Even after the fifth recycling, the synthetic adsorbent can still reach 616.90 mg/g adsorption capacity.