The invention provides a method for preparing a graft modification protein and an application thereof, belonging to the graft modification technical field. The invention introduces a method for the graft modification of the protein: an initiating agent, a chain transfer agent and a functional monomer are used to prepare a polymer chain with one end provided with the active functional group, and acatalyst is used to graft the amino-capped polymer onto the protein, and after the reaction, the modification protein grafted is separated out by steps of deposition, centrifugation, alcoholic extraction or alcohol washing and drying. The raft modification protein possesses of excellent characteristics of the protein as well as the amino-capped polymer, thereby providing the space for further widening the application of the graft modification protein; compared with the common protein, the graft modification protein with the grafted hydrophilic polymer has desirable solubility, surface hydrophobicity, emulsibility and foamability, so that the graft modification protein can be used as an emulsifying agent.