Abstract: Aiming at the problem of poor settlement effect of slime water in coal preparation plant, the settlement effect of slime water was improved by optimizing the settlement condition of slime water. Firstly, the industrial, particle size and XRD analysis were carried out on the slime water, and then the slime water settlement test was carried out to investigate the influence of the slime water concentration, pH and the amount of anionic polyacrylamide on the slime water settlement effect. On this basis, box-Behnken Design response surface method (RSM-BBD) was used to carry out conditional optimization tests, and a response surface regression model was established to study the influence of slime water concentration, pH, NPAM dosage and their interactions on the comprehensive index of slime water settlement. The results showed that the coal ash content was 59.46%, 90% of the coal slime particles were smaller than 26.85 μm, and the content of clay minerals was high. The concentration of slime water has the greatest influence on the comprehensive index, and the interaction between the concentration of slime water and NPAM dosage has the most significant influence on the comprehensive index; After optimization, the settlement conditions were as follows: coal slime water concentration was 45 g·L-1, pH was 9, NPAM dosage was 2.2 mL, and then the comprehensive index was 3.64 cm·s-1·NTU-1, which was very close to the predicted value of 3.68 cm·s-1·NTU-1.