Abstract: During the wet cleaning process, a large amount of high-muddy difficult-to-settle coal slurry water is produced. To solve this knotty problem, following an analysis of the causes leading to the difficulty in treatment of the slurry water and the problems encountered in the application of traditional slurry water settlement and clarification techniques, a general survey is made of the state-of-the-art of the new techniques which involves the mineral-hardness method, hydrophobic aggregation, external electric field assistance, microbial flocculation and magnetic flocculation, among others. Finally, the paper looks to the developing trend of such new techniques for treating difficult-to-settle coal slurry water.