The invention provides a preparation method of a regenerated cellulose based cross-linked modified nanofiltration membrane. The preparation method comprises the following steps: firstly, producing a cellulose membrane casting solution by adopting NMMO (N-methylmorpholine-N-oxide), propyl gallate and a cellulose membrane casting solution; secondly, preparing a regenerated cellulose membrane by adopting an immersion gel method, wherein the thickness of the membrane is 2mu m to 50mu m; then, preparing an ALG/CMC blended solution; taking the prepared regenerated cellulose membrane as a basic membrane and uniformly coating the basic membrane with the ALG/CMC (sodium alginate/carboxymethylcellulose sodium) blended solution; carrying out air drying for 12h to 36h at room temperature to obtain a composite cellulose membrane; immersing the obtained composite cellulose membrane into an epichlorohydrin ethanol solution and regulating the pH (Potential of Hydrogen) of the system to 9 to 12; carrying out cross-linking reaction for 4h to 24h under the condition that the temperature is 30 DEG C to 70 DEG C, so as to obtain the regenerated cellulose based cross-linked modified nanofiltration membrane. The preparation method provided by the invention has the advantages of simple preparation process, cheap raw materials and wide sources; the prepared regenerated cellulose based cross-linked modified nanofiltration membrane has the characteristic of high additional value and environment friendliness.