The work aims to carry out the impact test of single CrAlTiN coating prepared on the titanium alloy surface, so as to investigate and reveal the rules and mechanism of erosion damage on the titanium alloy surface. The single CrAlTiN coating was prepared on the TC4 titanium alloy surface by multi-arc ion plating and the erosion damage of the coating was simulated by firing a sphere projectile with the light gas gun at a nominal velocity of 300 m/s from different impact angles (30°, 45°, 60° and 90°). The impacted morphology was observed by scanning electro microscopy, and then the erosion damage mechanism was discussed according to the results of the element analysis. The erosion damage under 90° impact was mainly attributed to the compound effect of the crack generated from the impact and peeling of “liquid drop” on the surface. The erosion damage under 30° was similar with that under 45° and 60°, including two parts, namely the crack caused by the vertical impact and peeling of liquid drop on the surface and the friction damage caused by the tangential impact and the cladding materials resulted from the local temperature rise during the impact processing. The point 44 in the energy spectrum had two substances of Fe2O3 and TiN, which indicated that the coating at this point was desroyed and the damage included cutting wear, impact of steel ball and oxidative wear. At 300 m/s, the region with the most serious erosion damage is the contact location between the sphere and the coating; the sphere cladding material due to the local temperature is formed on the coating surface, and the rougher the coating surface is, the more the cladding materials are; and the erosion damage of coating is mainly attributed to the compound effects of the crack initiation due to the vertical impact and the tangential plough cutting action.