The invention provides a method for producing a cellulose-grafted polylactic acid copolymer from cellulose. The method comprises the following steps: (1) weighing a raw material, i.e., cellulose; (2) mixing the cellulose with organic base and an organic solvent; (3) introducing CO2 with a certain pressure into a mixed system obtained in the previous step and carrying out a reaction for a certain period of time so as to obtain a solution containing a cellulose-based CO2-reversible polyion compound; (4) adding a lactide reagent into the cellulose solution and carrying out a reaction in an inert gas atmosphere at 20 to 100 DEG C for 5 to 48 h so as to obtain a reaction mixture; (5) adding C1-3 lower fatty alcohol into the reaction mixture and filtering the reaction mixture containing lower fatty alcohol; and (6) subjecting a solid mixture obtained after filtering to purification so as to obtain the cellulose-grafted polylactic acid copolymer. The method provided by the invention has the advantages of simple process, low solvent cost, convenience in operation and no pollution.