The invention discloses a protein fiber reactive dye low-salt dyeing modification method and belongs to the technical field of modification of textile materials. The protein fiber reactive dye low-salt dyeing modification method comprises the following steps: immersing protein fiber into a buffer solution containing chitosan oligosaccharide, reacting at 80 to 90 DEG C for 45 to 60 minutes, takingout the protein fiber, washing the protein fiber with water, drying to obtain aminated protein fiber, and performing reactive dye low-salt dyeing on the aminated protein fiber. The invention providesa method for improving the dyeing property of the protein fiber on the reactive dye under the condition of low-salt concentration by performing cationic modification on the protein fiber by the chitosan oligosaccharide; compared with the unmodified wool, the dyeing percentage of the modified wool on the reactive dye and the K/S value are increased by 32 percent and 135 percent correspondingly. Compared with the traditional method, the method has the advantages that the chitosan oligosaccharide serves as a modifier and the modification condition is mild, non-toxic and easy to control; furthermore, the problems of chemical residues and environmental pollution caused by use of chemical reagents are avoided; and high practicability is achieved.