Abstract: The raw coal treated by Baiyan Coal Washery of Chongqing Songzao Coal & Electricity Co., Ltd., contains characteristically a high proportion of fine coal. In light of the specific situation, an analysis is made of the effect of scalping-out of coarser practices from thickener underflow on the operating parameters and targeted production indices of various process links. Practice shows that recirculating thickener underflow back to coarser slime recovery system may possibly reduce the load of filter pressing system, however, such an approach is unfavorable to clarification of circulating water and stability of qualified medium density. And as a result, the time required for the settling of fine slime in the thickener is much lengthened, affecting therefore the stable operation of coal washing systems.