In order to develop green and environmentally friendly hydrogel membranes for oil-water separation, this study extracted cellulose from waste poplar wood and employed a synergistic assembly strategy to construct a green cellulose-based hydrogel (CLH) membrane for oil-water separation. Lithium chloride (LiCl) was introduced as an active water-absorbing unit into the cellulose framework, and then polyvinyl alcohol (PVA) was used to encapsulate LiCl particles on the cellulose framework to prepare the CLH hydrogel. The preparation process was environmentally friendly and simple. The prepared CLH hydrogel membrane exhibited a laminar structure, overcoming the compressibility limitation of traditional hydrogels. Under the influence of gravity, the CLH hydrogel membrane achieved efficient separation of oil-water mixtures and oil-in-water emulsions. Moreover, the CLH hydrogel membrane demonstrated good stability, durability, and recyclability during the separation process. In short, the collaborative assembly strategy can not only effectively solve the problem of cellulose resource waste caused by waste wood production, but also can provide a new method for oil-water separation.