The invention discloses a method for preparing oxidized cellulose. The preparation method comprises the following steps: a, putting an oxidized cellulose material into inert solution; b, adding an oxidant into the inert solution, sealing the solution, stirring the solution for 10 to 12 hours by using a magnetic stirrer at the temperature of between 20 and 60 DEG C; c, taking the oxidized cellulose material out, and washing the oxidized cellulose material with purified water; d, drying the oxidized cellulose material by using a centrifugal machine, and then washing the oxidized cellulose material by cleaning solution; and e, drying the oxidized cellulose material to obtain a finished product. Because the inert solution is used as a reaction solvent, the oxidization reaction can be performed under the controllable conditions, the reaction is even, and the manufactured oxidized cellulose and oxidized regenerated cellulose products are stable and easy to store; and the reaction solvent and the oxidant can be reclaimed for recycle, so the method is economic and environment-friendly, and the production cost is greatly reduced.