Abstract: Aiming at investigating the deterioration of the coating on steel structure eroded in sandstorm, the erosion test to the coating on steel structure was conducted by using airflow jet with sand at low erosion-angle. The mass-loss measurement method was used to assess erosion degree of the coating. Microstructure of the erosion zone was analyzed to reveal the erosion mechanism of the coating. A formula for assessing the erosion degree of the coating was proposed. Results show that the mass-loss of coating increased with increasing sand dose and impact velocity. The main erosion mechanism was micro-cutting at a low erosion-angle and hardness of material was a decisive factor. Erosion is mainly compressive deformation at a high erosion-angle and material toughness played a decisive role. Because the coating had low hardness and high toughness, it was eroded severely at a low erosion-angle. The reliability of the assessment formula was verified to assess the erosion degree of the coating.