The work aims to study the damage characteristics and mechanism of TiN/Ti hard coatings with different thickness deposited on the aero-engine compressor blades under the impact of sand particles. Vertical cycling impact test of Si3N4 hard particle under constant kinetic energy was adopted. The influence of thickness on the impact damage of TiN/Ti coatings was investigated. The impact damage characteristics of coatings with different thickness were analyzed by dynamic response of coatings, energy absorption rates, contours of impact pit, H3/E2 values of coatings and damage morphologies. The stress distri-bution of coating under normal impact was obtained by ABAQUS software simulation. It was found that among the bilayer TiN/Ti coating of modulation 9∶1, the pit diameter of coating with 25 μm was the largest, about 382.49 μm, and 24.82% larger than the minimum pit diameter of coating with 20 μm. The pit depth of coating with 25 μm was the largest, about 8.17 μm and 49.91% larger than the minimum pit depth of coating with 15 μm. The contact peak force of coating with 5 μm was the largest, about 161.44 N and 26.16% larger than the minimum contact peak force of coating with 20 μm. There were three characteristics of impact pit damage: the fatigue spalling and fatigue wear in the central zone and intermediate zone, fatigue circular crack and fatigue spalling in peripheral zone and deformation of coating/substrate. Spalling was the main damage characteristic. With the increase of the coating thickness, the impact resistance of coating increases first and then decreases. The coating with 20 μm thickness shows the best anti-impact performance among different thickness. The stress gradient and cycling alternating tension-compression stress in the hard layer account for the fatigue circular crack and fatigue spalling and the high stress gradient in interface of hard and bonding layers accounts for the interface fatigue pilling.