Fluid shear plays a paramount role in flocculation. In present work, a fluidized bed flocculator with a decreasing fluid shear intensity in steps, called gradient fluidized bed (GFB) flocculator, was developed according to the self-preserving nature of floc size distribution and the flocculation kinetics. Then flocculation experiments were conducted to evaluate the performance of the GFB flocculator on flocculating coal-slime water in different flow rates. Results show that the flocculation of the GFB flocculator reducing the supernatant turbidity by 32% when compared with a pipe one, exhibiting obvious advantages. When the superficial velocity was 0.44 m/s, the velocity gradient along the height of the GFB decreased from 240 to 145 s(-1), contributing the best result that the flocs size up to 1 mm and the turbidity of the supernatant lower to 17 NTU. It can be concluded that GFB should be an efficient flocculator for flocculating coal-slime water when a reasonable apparent velocity is well conducted. (C) 2019 Elsevier B.V. All rights reserved.