The invention relates to a chemical-crosslinking-based cellulose-chitosan composite dressing and a preparation method thereof. The composite dressing comprises a silicane epoxide coupling agent, cellulose and chitosan or a chitosan derivative and has a uniform porous meshy structure, and the chitosan or the chitosan derivative uniformly coats the surface of a cellulose skeleton through crosslinking of the silicane epoxide coupling agent. The preparation method comprises the following steps: synthesizing a mixed suspension; and synthesizing the chemical-crosslinking-based cellulose-chitosan composite dressing. The preparation method is simple, easy to operate, low in cost and environmentally friendly. The obtained chemical-crosslinking-based cellulose-chitosan composite dressing has favorable mechanical property and toughness, is big in fluid absorption quantity and excellent in air permeability, prevents skin cells at a wound from being injured by digestion of small molecules in the using process, can promote blood coagulation and avoid wound infection, and therefore, has a wide application prospect in the medical dressing field.