In this study, waste crab shell was hydrothermally carbonized and then activated to prepare an effective and recyclable adsorbent. The adsorption performance of the adsorbent for different dyes was investigated through adsorption experiments, and the results showed that it had the largest adsorption performance for malachite green. Furthermore, the adsorption performance and mechanism of malachite green were investigated by static and dynamic adsorption method. The crab shell biochar could remove 6142.5 mg g-1 of malachite green within 3 minutes, indicating that the crab shell biochar could ultrarapid and highly efficient adsorb malachite green. In addition, the malachite green adsorbed on the crab shell biochar could be removed by calcination, which achieved the entire regeneration of the crab shell biochar. The adsorption of malachite green by crab shell biochar adsorbent conformed to the pseudosecond- order kinetic model, the Dubinin-Radushkevich and Langmuir isotherm adsorption model. Physical and chemical characterization indicated that the adsorption mechanism of malachite green included alkaline fading effect, hydrogen bonding and p-p interaction.