The invention discloses a method for preparing a silk fibroin sodium alginate composite fiber and belongs to the technical field of natural macromolecule composite materials. The method comprises thefollowing steps: firstly, mixing, stirring and dissolving silk fibroin with water, performing dialysis, and performing centrifugal separation so as to obtain a pretreated silk fibroin solution; mixingelastinase and the pretreated silk fibroin solution, adjusting the pH value, and performing constant-temperature stirring enzymolysis so as to obtain enzymatic hydrolysate; mixing phospholipid with the enzymatic hydrolysate, performing ultrasonic dispersion, further adding sodium alginate, plant essential oil and monosaccharide, performing a constant-temperature stirring reaction so as to obtaina reaction liquid, mixing the reaction liquid with Carbomer, performing a constant-temperature stirring reaction so as to obtain a spinning solution, performing vacuum defoaming, spinning, washing with water, and performing traction, coiling and drying, thereby obtaining the silk fibroin sodium alginate composite fiber. The silk fibroin sodium alginate composite fiber prepared by using the methodhas good mechanical properties.