The invention relates to a chitosan / KIT‑6 type silicon-based composite material and a preparation method and application thereof. The technical scheme adopted is: first dissolve an appropriate amount of P123 in water, and add concentrated hydrochloric acid, stir in a water bath overnight, then add n-butanol and stir, then add tetraethyl orthosilicate, after the reaction, pour the solution into the chitosan solution Add glutaraldehyde dropwise, continue to react for a period of time, transfer to an autoclave for hydrothermal reaction for a certain period of time, cool, filter with suction, wash until neutral, dry overnight, and perform Soxhlet extraction with acetone to obtain CS‑KIT‑ 6. Dissolve CS‑KIT‑6 in dimethyl sulfoxide, add appropriate amount of epichlorohydrin, microwave reaction, wash until neutral, dry overnight, then add a certain amount of polyethyleneimine solution and N,N‑ Dimethylformamide was subjected to microwave reaction, washed to neutrality, and dried overnight to obtain the product PEI‑CS‑KIT‑6. The composite material prepared by the invention can be used as an adsorbent for the adsorption of chromium in the water body, and has the characteristics of energy saving, environmental protection, high efficiency and the like.