A waterborne polyurethane is used as the main film-forming material to prepare a protective coating with good water resistance. The synthesis process of waterborne polyurethane is analyzed by orthogonal method. The influence of triethylamine and H2O content on the properties of the product is analyzed by testing the FTIR, storage time, exterior and water resistance. Then, the synthesis product is used as the base material, The polycarbodiimide and other additives are used to prepare waterborne coatings. The protective and strippable properties of the waterborne coating are analyzed by testing Shore hardness, adhesion, tensile strength, elongation at break, peel strength and water resistance. the waterborne polyurethane is successfully synthesized, and the optimum synthesis process of the self-emulsifying waterborne polyurethane is obtained. The coating processability and the coating performance are good, and the coating can be peeled off in one time. The coating has good water resistance: After soaking in room temperature for 48 h, the quality is basically unchanged, The tensile strength is changed from 37.7 MPa to 33.6 MPa, the elongation at break from 540% to 510%, and the Shore hardness is still for the 82HA; The addition of polycarbodiimide and other additives makes the coating has good peelability and water resistance, and the coating hardness of 82HA, the substrate can play a protective role.