Aiming at the durability deterioration of the coating of steel structure because of being eroded in sandstorm. through the erosion test to the coating of steel structure by airflow jet with sand at low erosion-angle, the mass-loss measurement method is used to assess erosion-wear degree of the coating, Observation of microstructure of the erosion zone using SEM to analyze the erosion-wear mechanism of the coating, and proposes a assessment formula for assessing the erosion-wear degree of the coating. Results show that the erosion-wear mechanism is that erosion is mainly micro-cutting role at low erosion-angle, materials hardness is decisive factor, and erosion is mainly compression deformation at high erosion-angle, materials toughness plays decisive role, as the coating is low hardness and high toughness materials, which is eroded more seriously at low erosion-angle. The reliability of the assessment formula is verified to assess the erosion-wear degree of the coating. The study will provide basis for exactly assessing the durability of steel structure.