Abstract: The easy detachment of coarse coal particle is the main factor that restricts the flotation of hard-to-float coarse particle slime. In order to explore the axial detachment law of hard-to-float coarse particle in the cylinder,using a homemade fluidized bed flotation column with an increased water flow at different axial positions above the flotation column feed opening,the apparent flow rate of the ascending water flow above the feed inlet of the flotation column was made to be greater than that of the coarse particle coal slime maximum settlement of the final velocity. Thereby,the coarse-grained slime was carried by the bubbles to the feedstock port into the foam product to reduce the loss of clean coal caused by coarse particles detachment above the feedstock port. The results show a linear relationship between the desorption rate of the hard-to-float coarse coal particles in the axial direction of the cylinder and the axial height of the cylinder,and the interface detachment accounts for approximately 40% of the total detachment rate,which proves that the flotation defects of difficult flotation particles are mainly due to large detachment probability. Flotation of difficult flotation particles can be effectively achieved by rising water flow above the feed inlet or lowering the column height a- bove the feed inlet.