The invention discloses a citric acid-chitosan-modified anticoagulation polyurethane blood dialysis membrane and a preparation method thereof. The membrane is of a hollow fibrous structure, and the inner surface and outer surface are dense cortical layers, and the middle is a porous supporting layer, so that the blood dialysis membrane is high in permeability and separating property and antibacterial property; the inner diameter is 160 to 250mu m; the membrane thickness is 30 to 50 mu m, and the ultrafiltration coefficient is 7.0 to 60 ml/m<2>.h.mmHg; citric acid-chitosan-modified anticoagulation polyurethane is taken as membrane materials, and in membrane solution, the percentage mass content of the modified anticoagulation polyurethane is 15 to 30%, and the percentage mass content of a solvent is 70 to 85%, and the blood dialysis membrane is prepared by using a nonsolvent induced phase separation method. The preparation process of the dialysis membrane is simple and easy to control, and the prepared membrane has good anticoagulant activity, biocompatibility and antibacterial property, and the clearance rates of urea, beta2-microglobulin and albumin are respectively 55 to 80%, 48 to 60%, and 2.5 to 9%, and the rate of resisting pathogenic escherichia coli is 99%.