The invention relates to a chitosan and/or chitosan derivative modified regenerated cellulose fiber. A preparation method of the cellulose fiber includes the steps: dissolving chitosan and/or chitosanderivative graft cellulose pulp to prepare spinning solution; spinning the spinning solution by a wet method or dry-jet wet method to prepare the chitosan and/or chitosan derivative modified regenerated cellulose fiber. Grafting reaction of chitosan and/or chitosan derivatives and cellulose pulp is implemented under the action of a cross-linking agent to prepare the chitosan and/or chitosan derivative graft cellulose pulp, and the finally prepared chitosan and/or chitosan derivative modified regenerated cellulose fiber mainly comprises a regenerated cellulose fiber substrate and chitosan and/or chitosan derivatives, the chitosan and/or chitosan derivatives are uniformly dispersed in the regenerated cellulose fiber substrate and uniformly dispersed on the surface of the regenerated cellulose fiber substrate, and chitosan and/or chitosan derivative molecular chains are connected with regenerated cellulose molecular chains through cross-linking agents. The preparation method is simple and easy, and the prepared fiber has good antibacterial properties, mechanical property and washing resistance.