Abstract: The slime water produced in the process of coal washing is difficult to settle due to its high suspended solids content and colloidal stability, which directly affects the efficiency and environmental compliance of the circulating water system of the coal preparation plant. In this paper, the slime water of Lijiahao Coal Preparation Plant is taken as the research object, and the key factors of difficult settlement of slime water in Lijiahao Coal Preparation Plant are systematically explored. It is found that the content of fine-grained clay minerals in the sample is high, the surface negative charge is significant, and the pore structure is complex. The optimization of the reagent system can significantly improve the sedimentation rate of coal slime water and the turbidity of the supernatant. The research results provide theoretical basis and technical reference for the efficient treatment of slime water in Lijiahao Coal Preparation Plant.