To clarify the erosion mechanism of multilayer TiAlN/Ti coatings on TC4 substrate, the paper provides a basis to improve the erosion resistance of TC4 alloy and prepare the coatings with excellent erosion resistance. TiAlN/Ti coatings with the same thickness and different layers are prepared on the surface of TC4 titanium alloy by magnetic filtration vacuum cathode arc (FCVA) and metal steam vacuum arc (MEVVA). The microstructure and mechanical property of TiAlN/Ti coating are characterized and analyzed by SEM, optical microscope and nano-indentation instrument. The erosion tests of TC4 titanium alloy and TiAlN/Ti coatings are carried out on the erosion test platform through the adjustment of parameters to simulate the dust environment. The erosion rate is calculated. The residual stress are characterized by proto-LXRD, the reosion morphology is analyzed by SEM, and the erosion mechanism is investigated. The test results show that the mass loss of TiAlN/Ti coatings with 4, 8 and 12 layers decreased by 86.9%, 91.3% and 94.0% respectively and the residual stress increases by 34 MPa, 135 MPa and 203 MPa. Concerning about the surface morphology of the erosion area, the erosion area of 4 layers coating is obviously exfoliated, the erosion area of 8 layers coating is partially exfoliated, and the erosion area of 12 layers coating is slightly exfoliated, which provides excellent protection for the substrate against erosion. MEVVA can significantly improve the adhesion between the coating and the matrix, and TiAlN/Ti coating could significantly improve the surface properties of the substrate. The more TiAlN/Ti layer number, the larger H3/E2 value, the better erosion resistance could be achieved.