The moisture contained in the material can be divided into two kinds: one is the intrinsic moisture, which exists in the pores of the material; but the external moisture, the water attached to the surface of the material, such as the mire, the rock fissure water, Fissure water, dusting equipment, spray water, pouring rain and other foggy days. External moisture content is proportional to the surface area of the material. Fine-grained material due to the large surface area, fine particles with external moisture is high. Internal moisture has no effect on the screening process, external moisture has a greater impact on the screening process. Containing high clay content that contains clay minerals, the material of the bond, even if the water is very low, but also easy to make the material bonded into a group, clogging the sieve under the sieve and sieve mesh.