How to determine the optimal water content range of the vertical roller mill feed is an important measure to improve the grinding efficiency, and its range depends on the following factors: 1. When the fluidity of the material is good, the moisture content of the material can be appropriately increased. After adding fly ash, with the increase of fluidity, the requirement of slag moisture content can be slightly expanded. 2. When the material is stored for too long, even if the water content is the same, the viscosity of the grinding paste is high. Some ten-year-old tailings ponds will grind paste, even if the water reaches 0.8% paste 3. The smaller the caster opening in the seal diaphragm section of the vertical mill, the easier it is to block, and the water content of the material is appropriately increased by increasing the caster opening 4. The vertical mill has large air volume, high wind speed, high internal temperature of the mill, and the moisture content of the material can be increased accordingly. In short, the enterprise should find a good humidity range and control it within the range according to the slag vertical mill type, material, and grinding process.