Abstract: There were often a great deal of foam in thickeners in Xinjulong coal preparation plant.To resolve this problem,the coal property,flotation reagent system and coal slurry treatment progress flow were researched.The results show that,the clay minerals in flotation feed lead to fine mud entrainment and deteriorate the flotation,improper flotation reagent system and coal slurry treatment flow make the flotation reagent leave a residue in thickeners,the low-ash coal brought by hydrocyclones overflow is separated with the action of residual flotation reagent in thickeners.The solutions were provided,such as preprocessing slurry before flotation in order to improve the flotation efficiency,draining the hydrocyclones overflow to flotation or thickener,making proper reagent system,adding baffle in thickener to block foam and extend fine slime settling time.