A chemically modified cellulose/alginate co-spun (seacell) fiber, a wound dressing made therefrom and a preparation method thereof. The seacell fiber is subject to a chemical modification through which a hydrophilic carboxymethyl group is introduced into the cellulose structure making the chemically modified seacell fiber more absorbent. The modified cellulose has a degree of substitution of 0.05-0.5; the seacell fiber has a linear density of 0.5-5 dtex and a fiber length of 5-180 mm. The seacell fiber has hygroscopic and gel-forming properties, while retaining its active ingredient of algae particles.