The surface treatment of the protected steel substrate is the basic process of the construction of the water-based fire retardant coating of the thin steel structure. Its purpose is to create a good condition for the adhesion of the coating to the surface of the steel substrate being protected and at the same time to improve and improve the properties of the coating. Steel surface treatment is the coating process to achieve good results a key link. The purpose of surface treatment: First, remove all kinds of dirt on the surface of the object to be coated, the coating and coated steel substrate surface is well attached to ensure that the coating has excellent performance. Dirt is divided into two types of inorganic and organic fouling, their presence not only affects the appearance of the coating, the serious will make the film into a piece off; Second, trimming the surface of the object to be protected, remove the existing defects to provide fire-retardant coating construction required Surface roughness, brushing when there is a good basis for the attachment. The practice shows that the suitable roughness of the surface of the object to be coated is 4 to 6 grade. Thirdly, different treatment methods are adopted for the different materials of the steel substrate to be protected so as to improve the adhesion and anti-corrosion ability of the coating. Surface treatment methods vary widely, should be based on the surface of steel substrate after being cleaned and smooth, the type and characteristics of dirt and pollution levels to choose from. Belong to the surface of the purification treatment degreasing, rust, in addition to the old paint; belongs to the chemical treatment of phosphating, passivation.